WO2016122086A1 - Transmission and reception device and method for wireless communication system - Google Patents

Abstract

A data transmission method for a station (STA) device in a LAN (wireless LAN) system is disclosed. The data transmission method for an STA device, according to the present invention, comprises the steps of: receiving a signal for another STA; counting the number of ACK frames if the received signal includes ACK frames; and adjusting a CCA level on the basis of the number of ACK frames counted for a specific amount of time.

Description

Transmission and reception apparatus and method of wireless communication system

The present invention relates to a wireless communication system, and more particularly, to wirelessly transmit data while adjusting a CCA level using at least one of the number of ACK frames or strength information of a received signal in a wireless local area network (LAN) communication system. A transmitting and receiving device of a communication system and a data transmission method thereof.

Wi-Fi is a Wireless Local Area Network (WLAN) technology that allows devices to access the Internet in the 2.4 GHz, 5 GHz, or 6 GHz frequency bands.

WLANs are based on the Institute of Electrical and Electronic Engineers (IEEE) 802.11 standard. The Wireless Next Generation Standing Committee (WNG SC) of IEEE 802.11 is an ad hoc committee that considers the next generation wireless local area network (WLAN) in the medium to long term.

IEEE 802.11n aims to increase the speed and reliability of networks and to extend the operating range of wireless networks. More specifically, IEEE 802.11n supports High Throughput (HT), which provides up to 600 Mbps data rate, and also supports both transmitter and receiver to minimize transmission errors and optimize data rates. It is based on Multiple Inputs and Multiple Outputs (MIMO) technology using multiple antennas.

As the popularity of WLAN and the applications diversify using it, the next generation WLAN system supporting Very High Throughput (VHT) is the next version of the IEEE 802.11n WLAN system. IEEE 802.11ac supports data processing speeds of 1 Gbps and higher via 80 MHz bandwidth transmission and / or higher bandwidth transmission (eg 200 MHz) and operates primarily in the 5 GHz band.

Recently, there is a need for a new WLAN system to support higher throughput than the data throughput supported by IEEE 802.11ac.

The scope of IEEE 802.11ax, often discussed in the next-generation WLAN study group called IEEE 802.11ax or High Efficiency (HEW) WLAN, is: 1) 802.11 physical layer and MAC in the 2.4 GHz and 5 GHz bands. (medium access control) layer enhancement, 2) spectral efficiency and area throughput improvement, 3) environments with interference sources, dense heterogeneous network environments, and high user loads. Such as improving performance in real indoor environments and outdoor environments, such as the environment.

Scenarios considered mainly in IEEE 802.11ax are dense environments with many access points (APs) and stations (STAs), and IEEE 802.11ax discusses spectral efficiency and area throughput improvement in such a situation. . In particular, there is an interest in improving the performance of the indoor environment as well as the outdoor environment, which is not much considered in the existing WLAN.

In IEEE 802.11ax, we are interested in scenarios such as wireless office, smart home, stadium, hotspot, and building / apartment. There is a discussion about improving system performance in dense environments with many STAs.

In the future, IEEE 802.11ax improves system performance in outdoor basic service set (OBSS) environment, outdoor environment performance, and cellular offloading rather than single link performance in one basic service set (BSS). Discussion is expected to be active. The directionality of IEEE 802.11ax means that next-generation WLANs will increasingly have a technology range similar to that of mobile communication. Considering the situation where mobile communication and WLAN technology are recently discussed in the small cell and direct-to-direct communication area, the technical and business of next-generation WLAN and mobile communication based on IEEE 802.11ax Convergence is expected to become more active.

As described above, a method for improving performance of the 802.11ax system, which is a next generation wireless LAN system, is actively being discussed. In particular, how to improve resource utilization efficiency over limited bandwidth is an important challenge in 802.11ax systems.

In the case of the existing system, the CCA was performed according to the same CCA level set by BSS. Therefore, spatial bandwidth reuse efficiency between BSSs is very low. This is because STAs belonging to different BSSs cannot detect and transmit signals by occupying the channel even if they can simultaneously transmit according to communication environment and channel quality.

Accordingly, the present invention is to propose a method for adjusting the CCA level and a data method accordingly, which can improve the spatial reuse efficiency of bandwidth.

In order to solve the above technical problem, an STA apparatus and a data transmission method of the STA apparatus of the WLAN system according to an embodiment of the present invention are proposed.

According to an embodiment of the present invention, a data transmission method of a STA (Station) device in a wireless LAN (WLAN) system includes: receiving a signal for another STA; Counting the number of ACK frames if the received signal comprises an ACK frame; Adjusting a CCA level based on the number of ACK frames counted during a particular time; When the received signal strength of the STA is greater than or equal to the adjusted CCA level, the wireless medium is detected in a busy condition. When the received signal strength is less than or equal to the adjusted CCA level, the wireless medium is idle. Detecting by; And initiating data transmission when the wireless medium is in idle condition.

In the data transmission method of the STA apparatus according to an embodiment of the present invention, adjusting the CCA level further includes increasing the CCA level when the number of the ACK frames for the other STA is greater than or equal to a certain number. do.

In the data transmission method of the STA device according to an embodiment of the present invention, the adjusting of the CCA level further comprises the step of reducing the CCA level when the number of the ACK frame for the other STA is less than a certain number. do.

In a data transmission method of an STA apparatus according to an embodiment of the present invention, the received signal includes a physical preamble, and the physical preamble further includes ACK frame identification information indicating whether the received signal corresponds to an ACK frame.

The data transmission method of the STA apparatus according to the embodiment of the present invention further includes the step of acquiring received signal strength information using the received signal for the other STA, the received signal strength in addition to the number of the ACK frame The CCA level can be adjusted based on the information.

In the data transmission method of the STA device according to an embodiment of the present invention, the reception strength information is a Received Channel Power Indicator (RSSI) parameter, when the RSSI parameter exceeds the threshold, the CCA level is maintained, and the RSSI If the parameter is greater than or equal to the threshold, the CCA level may be increased.

In addition, an STA (Station) device of a wireless LAN (WLAN) system according to an embodiment of the present invention, the RF (Radio Frequency) unit for transmitting and receiving a radio signal; And a processor for controlling the RF unit; Wherein the processor receives a signal for another STA and counts the number of the ACK frames when the received signal includes the ACK frame, and based on the number of the ACK frames counted for a specific time. Adjust a CCA level, detect a wireless medium in a busy condition if the received signal strength of the STA is above the adjusted CCA level, and if the received signal strength is below the adjusted CCA level, the wireless medium Is detected in an idle condition, and data transmission is initiated when the wireless medium is in an idle condition.

In the STA apparatus according to the embodiment of the present invention, the adjustment of the CCA level may be performed by increasing the CCA level when the number of the ACK frames for the other STA is greater than or equal to a certain number.

In the STA apparatus according to the embodiment of the present invention, the adjustment of the CCA level is performed by reducing the CCA level when the number of the ACK frames for the other STA is less than a certain number.

In the STA apparatus according to an embodiment of the present invention, the received signal may include a physical preamble, and the physical preamble may further include ACK frame identification information indicating whether the received signal corresponds to an ACK frame.

In the STA apparatus according to the embodiment of the present invention, the processor acquires received signal strength information using the received signal for the other STA, and based on the received signal strength information in addition to the number of the ACK frames. The CCA level can be adjusted.

In an STA apparatus according to an embodiment of the present invention, the reception strength information is a Received Channel Power Indicator (RSSI) parameter, and the processor maintains the CCA level when the RSSI parameter exceeds a threshold, and the RSSI If the parameter is greater than or equal to the threshold, the CCA level may be increased.

In addition, the data transmission method of the STA device of the wireless LAN (WLAN) system according to another embodiment of the present invention, the step of receiving a signal; Counting the number of ACK frames if the signal comprises an ACK frame; And transmitting CCA level control information based on the number of the ACK frames counted for a specific time, wherein the CCA level control information may be included in the physical preamble of the transmission signal of the STA and transmitted.

According to the present invention, the CCA level can be adjusted according to the counting number of the ACK frame. Accordingly, even adjacent STAs may perform signal transmission according to respective channel / transmit / receive power states, thereby improving bandwidth usage efficiency. In addition, spatial bandwidth reuse efficiency between STAs belonging to the OBSS may be improved. Since the adjustment of the CCA level is not fixed but is performed dynamically, the communication performance loss may be minimized by actively coping with the state change of the STAs and the channel environment change between the STAs.

Further, according to the present invention, unnecessary signal interference can be minimized as compared with the case of using only the ACK frame by using the strength information of the received signal as well as the counting of the ACK frame as the basis of the CCA level adjustment. In other words, the transmission / reception channel at the cell edge may prevent or minimize the increase of interference due to CCA adjustment for the STA that is poor.

1 is a diagram illustrating an example of an IEEE 802.11 system to which the present invention can be applied.

2 is a diagram illustrating a structure of a layer architecture of an IEEE 802.11 system to which the present invention may be applied.

3 illustrates a non-HT format PPDU and a HT format PPDU of a wireless communication system to which the present invention can be applied.

4 illustrates a VHT format PPDU format of a wireless communication system to which the present invention can be applied.

5 is a diagram illustrating a constellation for distinguishing a format of a PPDU of a wireless communication system to which the present invention can be applied.

6 illustrates a MAC frame format of an IEEE 802.11 system to which the present invention can be applied.

FIG. 7 is a diagram illustrating a Frame Control field in a MAC frame in a wireless communication system to which the present invention can be applied.

8 illustrates the VHT format of the HT Control field in a wireless communication system to which the present invention can be applied.

9 is a diagram for explaining an arbitrary backoff period and a frame transmission procedure in a wireless communication system to which the present invention can be applied.

10 is a diagram illustrating an IFS relationship in a wireless communication system to which the present invention can be applied.

11 is a diagram illustrating a downlink MU-MIMO transmission process in a wireless communication system to which the present invention can be applied.

12 illustrates a High Efficiency (HE) format PPDU according to an embodiment of the present invention.

13 is a diagram illustrating an HE format PPDU according to an embodiment of the present invention.

14 is a diagram illustrating an HE format PPDU according to an embodiment of the present invention.

15 is a diagram illustrating a HE format PPDU according to an embodiment of the present invention.

16 is a conceptual diagram illustrating a method of performing CCA according to an embodiment of the present invention.

17 is a conceptual diagram illustrating a method for adjusting CCA levels according to an embodiment of the present invention.

18 is a conceptual diagram illustrating a method for adjusting CCA levels according to another embodiment of the present invention.

19 is a conceptual diagram illustrating a method for adjusting CCA levels according to another embodiment of the present invention.

20 illustrates a STA apparatus according to an embodiment of the present invention.

21 illustrates a data transmission method of an STA apparatus according to an embodiment of the present invention.

22 illustrates a data transmission method of an STA 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 may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention.

Specific terms used in the following description are provided to help the understanding of the present invention, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present invention.

The following techniques are code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and NOMA It can be used in various radio access systems such as non-orthogonal multiple access. CDMA may be implemented by a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as global system for mobile communications (GSM) / general packet radio service (GPRS) / enhanced data rates for GSM evolution (EDGE). OFDMA can be implemented with wireless technologies such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.20 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like. UTRA is part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (advanced) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by standard documents disclosed in at least one of the wireless access systems IEEE 802, 3GPP and 3GPP2. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all terms disclosed in the present document can be described by the above standard document.

For clarity, the following description focuses on IEEE 802.11 systems, but the technical features of the present invention are not limited thereto.

System general

1 is a diagram illustrating an example of an IEEE 802.11 system to which the present invention can be applied.

The IEEE 802.11 structure may be composed of a plurality of components, and a wireless communication system supporting a station (STA) station mobility that is transparent to a higher layer may be provided by their interaction. . A basic service set (BSS) may correspond to a basic building block in an IEEE 802.11 system.

In FIG. 1, there are three BSSs (BSS 1 to BSS 3) and two STAs are included as members of each BSS (STA 1 and STA 2 are included in BSS 1, and STA 3 and STA 4 are BSS 2. Included in, and STA 5 and STA 6 are included in BSS 3) by way of example.

In FIG. 1, an ellipse representing a BSS may be understood to represent a coverage area where STAs included in the BSS maintain communication. This area may be referred to as a basic service area (BSA). When the STA moves out of the BSA, the STA cannot directly communicate with other STAs in the BSA.

The most basic type of BSS in an IEEE 802.11 system is an independent BSS (IBSS). For example, the IBSS may have a minimal form consisting of only two STAs. In addition, BSS 3 of FIG. 1, which is the simplest form and other components are omitted, may correspond to a representative example of the IBSS. This configuration is possible when STAs can communicate directly. In addition, this type of LAN may not be configured in advance, but may be configured when a LAN is required, which may be referred to as an ad-hoc network.

The membership of the STA in the BSS may be dynamically changed by turning the STA on or off, the STA entering or exiting the BSS region, or the like. In order to become a member of the BSS, the STA may join the BSS using a synchronization process. In order to access all services of the BSS infrastructure, the STA must be associated with the BSS. This association may be set up dynamically and may include the use of a Distribution System Service (DSS).

The direct STA-to-STA distance in an 802.11 system may be limited by physical layer (PHY) performance. In some cases, this distance limit may be sufficient, but in some cases, communication between STAs over longer distances may be required. A distribution system (DS) may be configured to support extended coverage.

DS refers to a structure in which BSSs are interconnected. Specifically, instead of the BSS independently as shown in FIG. 1, the BSS may exist as an extended type component of a network composed of a plurality of BSSs.

DS is a logical concept and can be specified by the characteristics of the Distribution System Medium (DSM). In this regard, the IEEE 802.11 standard logically distinguishes between wireless medium (WM) and distribution system medium (DSM). Each logical medium is used for a different purpose and is used by different components. The definition of the IEEE 802.11 standard does not limit these media to the same or to different ones. In this way, the plurality of media are logically different, and thus the flexibility of the structure of the IEEE 802.11 system (DS structure or other network structure) can be described. That is, the IEEE 802.11 system structure can be implemented in various ways, the corresponding system structure can be specified independently by the physical characteristics of each implementation.

The DS may support mobile devices by providing seamless integration of multiple BSSs and providing logical services for handling addresses to destinations.

The AP means an entity that enables access to the DS through the WM to the associated STAs and has STA functionality. Data movement between the BSS and the DS may be performed through the AP. For example, STA 2 and STA 3 illustrated in FIG. 1 have a functionality of STA, and provide a function of allowing associated STAs STA 1 and STA 4 to access the DS. In addition, since all APs basically correspond to STAs, all APs are addressable entities. The address used by the AP for communication on the WM and the address used by the AP for communication on the DSM need not necessarily be the same.

Data transmitted from one of the STAs associated with an AP to the STA address of that AP may always be received at an uncontrolled port and processed by an IEEE 802.1X port access entity. In addition, when a controlled port is authenticated, transmission data (or frame) may be transmitted to the DS.

A wireless network of arbitrary size and complexity may be composed of DS and BSSs. In an IEEE 802.11 system, this type of network is referred to as an extended service set (ESS) network. The ESS may correspond to a set of BSSs connected to one DS. However, the ESS does not include a DS. The ESS network is characterized by what appears to be an IBSS network at the Logical Link Control (LLC) layer. STAs included in the ESS may communicate with each other, and mobile STAs may move from one BSS to another BSS (within the same ESS) transparently to the LLC.

In the IEEE 802.11 system, nothing is assumed about the relative physical location of the BSSs in FIG. 1, and all of the following forms are possible.

Specifically, BSSs can be partially overlapped, which is the form generally used to provide continuous coverage. Also, the BSSs may not be physically connected, and logically there is no limit to the distance between the BSSs. In addition, the BSSs can be located at the same physical location, which can be used to provide redundancy. In addition, one (or more) IBSS or ESS networks may be physically present in the same space as one or more ESS networks. This may be necessary if the ad-hoc network is operating at the location of the ESS network, if the IEEE 802.11 networks are physically overlapped by different organizations, or if two or more different access and security policies are required at the same location. It may correspond to an ESS network type in a case.

In a WLAN system, an STA is a device that operates according to Medium Access Control (MAC) / PHY regulations of IEEE 802.11. As long as the function of the STA is not distinguished from the AP individually, the STA may include an AP STA and a non-AP STA. However, when communication is performed between the STA and the AP, the STA may be understood as a non-AP STA. In the example of FIG. 1, STA 1, STA 4, STA 5, and STA 6 correspond to non-AP STAs, and STA 2 and STA 3 correspond to AP STAs.

Non-AP STAs generally correspond to devices that users directly handle, such as laptop computers and mobile phones. In the following description, a non-AP STA includes a wireless device, a terminal, a user equipment (UE), a mobile station (MS), a mobile terminal, and a wireless terminal. ), A wireless transmit / receive unit (WTRU), a network interface device (network interface device), a machine-type communication (MTC) device, a machine-to-machine (M2M) device, or the like.

In addition, the AP is a base station (BS), Node-B (Node-B), evolved Node-B (eNB), and Base Transceiver System (BTS) in other wireless communication fields. , A concept corresponding to a femto base station (Femto BS).

Hereinafter, in the present specification, downlink (DL) means communication from the AP to the non-AP STA, and uplink (UL) means communication from the non-AP STA to the AP. In downlink, the transmitter may be part of an AP and the receiver may be part of a non-AP STA. In uplink, a transmitter may be part of a non-AP STA and a receiver may be part of an AP.

2 is a diagram illustrating a structure of a layer architecture of an IEEE 802.11 system to which the present invention may be applied.

Referring to FIG. 2, the layer architecture of the IEEE 802.11 system may include a MAC sublayer and a PHY sublayer.

The PHY sublayer may be divided into a Physical Layer Convergence Procedure (PLCP) entity and a Physical Medium Dependent (PMD) entity. In this case, the PLCP entity plays a role of connecting a data frame with a MAC sublayer, and the PMD entity plays a role of wirelessly transmitting and receiving data with two or more STAs.

Both the MAC sublayer and the PHY sublayer may include a management entity, which may be referred to as a MAC sublayer management entity (MLME) and a PHY sublayer management entity (PLME), respectively. have. These management entities provide layer management service interfaces through the operation of layer management functions. The MLME may be connected to the PLME to perform management operations of the MAC sublayer, and likewise the PLME may be connected to the MLME to perform management operations of the PHY sublayer.

In order to provide correct MAC operation, a Station Management Entity (SME) may be present in each STA. The SME is a management entity independent of each layer. The SME collects layer-based state information from MLME and PLME or sets values of specific parameters of each layer. The SME can perform these functions on behalf of general system management entities and implement standard management protocols.

MLME, PLME and SME can interact in a variety of ways based on primitives. Specifically, the XX-GET.request primitive is used to request the value of a Management Information Base attribute (MIB attribute), and the XX-GET.confirm primitive, if the status is 'SUCCESS', returns the value of that MIB attribute. Otherwise, it returns with an error indication in the status field. The XX-SET.request primitive is used to request that a specified MIB attribute be set to a given value. If the MIB attribute is meant for a particular action, this request requests the execution of that particular action. And, if the state is 'SUCCESS' XX-SET.confirm primitive, it means that the specified MIB attribute is set to the requested value. In other cases, the status field indicates an error condition. If this MIB attribute means a specific operation, this primitive can confirm that the operation was performed.

The operation in each sublayer is briefly described as follows.

The MAC sublayer includes a MAC header and a frame check sequence (FCS) in a MAC Service Data Unit (MSDU) or a fragment of an MSDU received from an upper layer (eg, an LLC layer). A sequence is attached to generate one or more MAC Protocol Data Units (MPDUs). The generated MPDU is delivered to the PHY sublayer.

When an aggregated MSDU (A-MSDU) scheme is used, a plurality of MSDUs may be merged into a single A-MSDU (aggregated MSDU). The MSDU merging operation may be performed at the MAC upper layer. The A-MSDU is delivered to the PHY sublayer as a single MPDU (if not fragmented).

The PHY sublayer generates a physical protocol data unit (PPDU) by adding an additional field including information required by a physical layer transceiver to a physical service data unit (PSDU) received from the MAC sublayer. . PPDUs are transmitted over wireless media.

The PSDU is substantially the same as the MPDU since the PHY sublayer is received from the MAC sublayer and the MPDU is transmitted by the MAC sublayer to the PHY sublayer.

When an aggregated MPDU (A-MPDU) scheme is used, a plurality of MPDUs (where each MPDU may carry an A-MSDU) may be merged into a single A-MPDU. The MPDU merging operation may be performed at the MAC lower layer. A-MPDUs may be merged with various types of MPDUs (eg, QoS data, Acknowledge (ACK), Block ACK (BlockAck), etc.). The PHY sublayer receives the A-MPDU as a single PSDU from the MAC sublayer. That is, the PSDU is composed of a plurality of MPDUs. Thus, A-MPDUs are transmitted over the wireless medium in a single PPDU.

PPDU Physical Protocol Data Unit Format

Physical Protocol Data Unit (PPDU) refers to a block of data generated at the physical layer. Hereinafter, a PPDU format will be described based on an IEEE 802.11 WLAN system to which the present invention can be applied.

3 illustrates a non-HT format PPDU and a HT format PPDU of a wireless communication system to which the present invention can be applied.

3A illustrates a non-HT format PPDU for supporting an IEEE 802.11a / g system. Non-HT PPDUs may also be referred to as legacy PPDUs.

Referring to (a) of FIG. 3, the non-HT format PPDU includes an L-STF (Legacy (or Non-HT) Short Training field), L-LTF (Legacy (or, Non-HT) Long Training field) and It consists of a legacy format preamble and a data field composed of L-SIG (Legacy (or Non-HT) SIGNAL) field.

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

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

The L-SIG field may be used to transmit control information for demodulation and decoding of the data field.

The L-SIG field consists of a 4-bit Rate field, 1-bit Reserved bit, 12-bit Length field, 1-bit parity bit, and 6-bit Signal Tail field. Can be.

The rate field contains rate information, and the length field indicates the number of octets of the PSDU.

3B illustrates an HT-mixed format PPDU (HTDU) for supporting both an IEEE 802.11n system and an IEEE 802.11a / g system.

Referring to FIG. 3B, the HT mixed format PPDU includes a legacy format preamble including an L-STF, L-LTF, and L-SIG fields, an HT-SIG (HT-Signal) field, and an HT-STF (HT Short). Training field), HT-formatted preamble and data field including HT-LTF (HT Long Training field).

Since the L-STF, L-LTF, and L-SIG fields mean legacy fields for backward compatibility, they are the same as non-HT formats from L-STF to L-SIG fields. Even if the L-STA receives the HT mixed PPDU, the L-STA may interpret the data field through the L-LTF, L-LTF and L-SIG fields. However, the L-LTF may further include information for channel estimation that the HT-STA performs to receive the HT mixed PPDU and demodulate the L-SIG field and the HT-SIG field.

The HT-STA may know that it is an HT-mixed format PPDU using the HT-SIG field following the legacy field, and may decode the data field based on the HT-STA.

The HT-LTF field may be used for channel estimation for demodulation of the data field. Since IEEE 802.11n supports Single-User Multi-Input and Multi-Output (SU-MIMO), a plurality of HT-LTF fields may be configured for channel estimation for each data field transmitted in a plurality of spatial streams.

The HT-LTF field includes data HT-LTF used for channel estimation for spatial streams and extension HT-LTF (additional used for full channel sounding). It can be configured as. Accordingly, the plurality of HT-LTFs may be equal to or greater than the number of spatial streams transmitted.

In the HT-mixed format PPDU, the L-STF, L-LTF, and L-SIG fields are transmitted first in order to receive the L-STA and acquire data. Thereafter, the HT-SIG field is transmitted for demodulation and decoding of data transmitted for the HT-STA.

The HT-SIG field is transmitted without performing beamforming so that the L-STA and HT-STA can receive the corresponding PPDU to acquire data, and then the HT-STF, HT-LTF and data fields transmitted are precoded. Wireless signal transmission is performed through. In this case, the HT-STF field is transmitted to allow the STA to perform precoding to take into account the variable power due to precoding, and then the plurality of HT-LTF and data fields after that.

3 (c) illustrates an HT-GF format PPDU (HT-GF) for supporting only an IEEE 802.11n system.

Referring to FIG. 3C, the HT-GF format PPDU includes HT-GF-STF, HT-LTF1, HT-SIG field, a plurality of HT-LTF2 and data fields.

HT-GF-STF is used for frame timing acquisition and AGC.

HT-LTF1 is used for channel estimation.

The HT-SIG field is used for demodulation and decoding of the data field.

HT-LTF2 is used for channel estimation for demodulation of data fields. Similarly, since HT-STA uses SU-MIMO, channel estimation is required for each data field transmitted in a plurality of spatial streams, and thus HT-LTF2 may be configured in plural.

The plurality of HT-LTF2 may be configured of a plurality of Data HT-LTF and a plurality of extended HT-LTF similarly to the HT-LTF field of the HT mixed PPDU.

In (a) to (c) of FIG. 3, the data field is a payload, and includes a service field, a SERVICE field, a scrambled PSDU field, tail bits, and padding bits. It may include. All bits of the data field are scrambled.

3 (d) shows a service field included in a data field. The service field has 20 bits. Each bit is assigned from 0 to 15, and transmitted sequentially from bit 0. Bits 0 to 6 are set to 0 and used to synchronize the descrambler in the receiver.

The IEEE 802.11ac WLAN system supports downlink multi-user multiple input multiple output (MU-MIMO) transmission in which a plurality of STAs simultaneously access a channel in order to efficiently use a wireless channel. According to the MU-MIMO transmission scheme, the AP may simultaneously transmit packets to one or more STAs that are paired with MIMO.

DL MU transmission (downlink multi-user transmission) refers to a technology in which an AP transmits a PPDU to a plurality of non-AP STAs through the same time resource through one or more antennas.

Hereinafter, the MU PPDU refers to a PPDU that delivers one or more PSDUs for one or more STAs using MU-MIMO technology or OFDMA technology. The SU PPDU means a PPDU having a format in which only one PSDU can be delivered or in which no PSDU exists.

The size of control information transmitted to the STA may be relatively large compared to the size of 802.11n control information for MU-MIMO transmission. An example of control information additionally required for MU-MIMO support includes information indicating the number of spatial streams received by each STA, information related to modulation and coding of data transmitted to each STA, and the like. Can be.

Therefore, when MU-MIMO transmission is performed to simultaneously provide data services to a plurality of STAs, the size of transmitted control information may be increased according to the number of receiving STAs.

In order to efficiently transmit the increased size of the control information, a plurality of control information required for MU-MIMO transmission is required separately for common control information common to all STAs and specific STAs. The data may be transmitted by being divided into two types of information of dedicated control information.

4 illustrates a VHT format PPDU format of a wireless communication system to which the present invention can be applied.

4 (a) illustrates a VHT format PPDU (VHT format PPDU) for supporting an IEEE 802.11ac system.

Referring to FIG. 4A, a VHT format PPDU includes a legacy format preamble including a L-STF, L-LTF, and L-SIG fields, a VHT-SIG-A (VHT-Signal-A) field, and a VHT-STF ( A VHT format preamble and a data field including a VHT Short Training field (VHT-LTF), a VHT Long Training field (VHT-LTF), and a VHT-SIG-B (VHT-Signal-B) field.

Since L-STF, L-LTF, and L-SIG mean legacy fields for backward compatibility, they are the same as non-HT formats from L-STF to L-SIG fields. However, the L-LTF may further include information for channel estimation to be performed to demodulate the L-SIG field and the VHT-SIG-A field.

The L-STF, L-LTF, L-SIG field, and VHT-SIG-A field may be repeatedly transmitted in 20 MHz channel units. For example, when a PPDU is transmitted on four 20 MHz channels (i.e., 80 MHz bandwidth), the L-STF, L-LTF, L-SIG field, and VHT-SIG-A field are repeatedly transmitted on every 20 MHz channel. Can be.

The VHT-STA may know that it is a VHT format PPDU using the VHT-SIG-A field following the legacy field, and may decode the data field based on the VHT-STA.

In the VHT format PPDU, the L-STF, L-LTF and L-SIG fields are transmitted first in order to receive the L-STA and acquire data. Thereafter, the VHT-SIG-A field is transmitted for demodulation and decoding of data transmitted for the VHT-STA.

The VHT-SIG-A field is a field for transmitting control information common to the AP and the MIMO paired VHT STAs, and includes control information for interpreting the received VHT format PPDU.

The VHT-SIG-A field may include a VHT-SIG-A1 field and a VHT-SIG-A2 field.

The VHT-SIG-A1 field includes information on channel bandwidth (BW) used, whether space time block coding (STBC) is applied, and group identification information for indicating a group of STAs grouped in MU-MIMO. Group ID (Group Identifier), information about the number of space-time streams (NSTS) / Partial AID (Partial Association Identifier) and Transmit power save forbidden information. can do. Here, the Group ID means an identifier assigned to the STA group to be transmitted to support MU-MIMO transmission, and may indicate whether the currently used MIMO transmission method is MU-MIMO or SU-MIMO.

The VHT-SIG-A2 field contains information on whether a short guard interval (GI) is used, forward error correction (FEC) information, information on modulation and coding scheme (MCS) for a single user, and multiple information. Information on the type of channel coding for the user, beamforming-related information, redundancy bits for cyclic redundancy checking (CRC), tail bits of convolutional decoder, and the like. Can be.

VHT-STF is used to improve the performance of AGC estimation in MIMO transmission.

VHT-LTF is used by the VHT-STA to estimate the MIMO channel. Since the VHT WLAN system supports MU-MIMO, the VHT-LTF may be set as many as the number of spatial streams in which a PPDU is transmitted. In addition, if full channel sounding is supported, the number of VHT-LTFs may be greater.

The VHT-SIG-B field includes dedicated control information required for a plurality of MU-MIMO paired VHT-STAs to receive a PPDU and acquire data. Therefore, the VHT-STA may be designed to decode the VHT-SIG-B field only when the common control information included in the VHT-SIG-A field indicates the MU-MIMO transmission currently received. . On the other hand, if the common control information indicates that the currently received PPDU is for a single VHT-STA (including SU-MIMO), the STA may be designed not to decode the VHT-SIG-B field.

The VHT-SIG-B field includes a VHT-SIG-B length field, a VHT-MCS field, a reserved field, and a tail field.

The VHT-SIG-B Length field indicates the length of the A-MPDU (before end-of-frame padding). The VHT-MCS field includes information on modulation, encoding, and rate-matching of each VHT-STA.

The size of the VHT-SIG-B field may vary depending on the type of MIMO transmission (MU-MIMO or SU-MIMO) and the channel bandwidth used for PPDU transmission.

4 (b) illustrates the VHT-SIG-B field according to the PPDU transmission bandwidth.

Referring to FIG. 4B, in the 40 MHz transmission, the VHT-SIG-B bits are repeated twice. For an 80 MHz transmission, the VHT-SIG-B bits are repeated four times and pad bits set to zero are attached.

For 200 MHz transmission and 80 + 80 MHz, first the VHT-SIG-B bits are repeated four times, as with the 80 MHz transmission, and pad bits set to zero are attached. Then, all 117 bits are repeated again.

In order to transmit a PPDU of the same size to STAs paired to an AP in a system supporting MU-MIMO, information indicating a bit size of a data field constituting the PPDU and / or indicating a bit stream size constituting a specific field May be included in the VHT-SIG-A field.

However, the L-SIG field may be used to effectively use the PPDU format. In order to transmit the same size PPDU to all STAs, a length field and a rate field included in the L-SIG field and transmitted may be used to provide necessary information. In this case, since the MAC Protocol Data Unit (MPDU) and / or Aggregate MAC Protocol Data Unit (A-MPDU) are set based on the bytes (or octets) of the MAC layer, additional padding is applied at the physical layer. May be required.

In FIG. 4, the data field is a payload and may include a service field, a scrambled PSDU, tail bits, and padding bits.

Since the formats of various PPDUs are mixed and used as described above, the STA must be able to distinguish the formats of the received PPDUs.

Here, the meaning of distinguishing a PPDU (or meaning of distinguishing a PPDU format) may have various meanings. For example, the meaning of identifying the PPDU may include determining whether the received PPDU is a PPDU that can be decoded (or interpreted) by the STA. In addition, the meaning of distinguishing the PPDU may mean determining whether the received PPDU is a PPDU supported by the STA. In addition, the meaning of distinguishing the PPDU may also be interpreted to mean what information is transmitted through the received PPDU.

This will be described in more detail with reference to the drawings below.

5 is a diagram illustrating a constellation for distinguishing a format of a PPDU of a wireless communication system to which the present invention can be applied.

FIG. 5 (a) illustrates the constellation of the L-SIG field included in the non-HT format PPDU, FIG. 5 (b) illustrates the phase rotation for HT mixed format PPDU detection, 5 (c) illustrates phase rotation for VHT format PPDU detection.

Constellation of OFDM symbols transmitted after the L-SIG field and the L-SIG field in order for the STA to classify non-HT format PPDUs, HT-GF format PPDUs, HT mixed format PPDUs, and VHT format PPDUs. Phase is used. That is, the STA may distinguish the PPDU format based on the phase of the constellation of the OFDM symbol transmitted after the L-SIG field and / or the L-SIG field of the received PPDU.

Referring to FIG. 5 (a), binary phase shift keying (BPSK) is used for an OFDM symbol constituting the L-SIG field.

First, in order to distinguish the HT-GF format PPDU, when the first SIG field is detected in the received PPDU, the STA determines whether it is an L-SIG field. That is, the STA tries to decode based on the constellation as shown in the example of FIG. If the STA fails to decode, it may be determined that the corresponding PPDU is an HT-GF format PPDU.

Next, in order to classify non-HT format PPDUs, HT mixed format PPDUs, and VHT format PPDUs, the phase of the constellation of OFDM symbols transmitted after the L-SIG field may be used. That is, the modulation method of OFDM symbols transmitted after the L-SIG field may be different, and the STA may distinguish the PPDU format based on the modulation method for the field after the L-SIG field of the received PPDU.

Referring to FIG. 5B, in order to distinguish the HT mixed format PPDU, the phase of two OFDM symbols transmitted after the L-SIG field in the HT mixed format PPDU may be used.

More specifically, the phases of OFDM symbol # 1 and OFDM symbol # 2 corresponding to the HT-SIG field transmitted after the L-SIG field in the HT mixed format PPDU are rotated by 90 degrees in the counterclockwise direction. That is, quadrature binary phase shift keying (QBPSK) is used as a modulation method for OFDM symbol # 1 and OFDM symbol # 2. The QBPSK constellation may be a constellation rotated by 90 degrees in a counterclockwise direction based on the BPSK constellation.

The STA attempts to decode the first OFDM symbol and the second OFDM symbol corresponding to the HT-SIG field transmitted after the L-SIG field of the received PPDU based on the properties as shown in the example of FIG. 5 (b). If the STA succeeds in decoding, it is determined that the corresponding PPDU is an HT format PPDU.

Next, in order to distinguish between the non-HT format PPDU and the VHT format PPDU, the phase of the constellation of the OFDM symbol transmitted after the L-SIG field may be used.

Referring to FIG. 5C, in order to classify the VHT format PPDU, the phase of two OFDM symbols transmitted after the L-SIG field in the VHT format PPDU may be used.

More specifically, the phase of the OFDM symbol # 1 corresponding to the VHT-SIG-A field after the L-SIG field in the VHT format PPDU is not rotated, but the phase of the OFDM symbol # 2 is rotated by 90 degrees counterclockwise. . That is, BPSK is used for the modulation method for OFDM symbol # 1 and QBPSK is used for the modulation method for OFDM symbol # 2.

The STA attempts to decode the first OFDM symbol and the second OFDM symbol corresponding to the VHT-SIG field transmitted after the L-SIG field of the received PPDU based on the properties as illustrated in FIG. 5 (c). If the STA succeeds in decoding, it may be determined that the corresponding PPDU is a VHT format PPDU.

On the other hand, if decoding fails, the STA may determine that the corresponding PPDU is a non-HT format PPDU.

MAC frame format

6 illustrates a MAC frame format of an IEEE 802.11 system to which the present invention can be applied.

Referring to FIG. 6, a MAC frame (ie, an MPDU) includes a MAC header, a frame body, and a frame check sequence (FCS).

MAC Header includes Frame Control field, Duration / ID field, Address 1 field, Address 2 field, Address 3 field, Sequence control It is defined as an area including a Control field, an Address 4 field, a QoS Control field, and an HT Control field.

The Frame Control field includes information on the MAC frame characteristic. A detailed description of the Frame Control field will be given later.

The Duration / ID field may be implemented to have different values depending on the type and subtype of the corresponding MAC frame.

If the type and subtype of the corresponding MAC frame is a PS-Poll frame for power save (PS) operation, the Duration / ID field is an AID (association identifier) of the STA that transmitted the frame. It may be set to include. Otherwise, the Duration / ID field may be set to have a specific duration value according to the type and subtype of the corresponding MAC frame. In addition, when the frame is an MPDU included in an A-MPDU format, the Duration / ID fields included in the MAC header may be set to have the same value.

The Address 1 to Address 4 fields include a BSSID, a source address (SA), a destination address (DA), a transmission address (TA) indicating a transmission STA address, and a reception address indicating a destination STA address (TA). RA: It is used to indicate Receiving Address.

Meanwhile, the address field implemented as a TA field may be set to a bandwidth signaling TA value, in which case, the TA field may indicate that the corresponding MAC frame contains additional information in the scrambling sequence. The bandwidth signaling TA may be represented by the MAC address of the STA transmitting the corresponding MAC frame, but the Individual / Group bit included in the MAC address may be set to a specific value (for example, '1'). Can be.

The Sequence Control field is set to include a sequence number and a fragment number. The sequence number may indicate a sequence number allocated to the corresponding MAC frame. The fragment number may indicate the number of each fragment of the corresponding MAC frame.

The QoS Control field contains information related to QoS. The QoS Control field may be included when indicating a QoS data frame in a subtype subfield.

The HT Control field includes control information related to the HT and / or VHT transmission / reception schemes. The HT Control field is included in the Control Wrapper frame. In addition, it exists in the QoS data frame and the management frame in which the order subfield value is 1.

The frame body is defined as a MAC payload, and data to be transmitted in a higher layer is located, and has a variable size. For example, the maximum MPDU size may be 11454 octets, and the maximum PPDU size may be 5.484 ms.

FCS is defined as a MAC footer and is used for error detection of MAC frames.

The first three fields (Frame Control field, Duration / ID field and Address 1 field) and the last field (FCS field) constitute the minimum frame format and are present in every frame. Other fields may exist only in a specific frame type.

FIG. 7 is a diagram illustrating a Frame Control field in a MAC frame in a wireless communication system to which the present invention can be applied.

Referring to FIG. 7, the Frame Control field includes a Protocol Version subfield, a Type subfield, a Subtype subfield, a To DS subfield, a From DS subfield, and more fragments. A subfield, a retry subfield, a power management subfield, a more data subfield, a protected frame subfield, and an order subfield.

The Protocol Version subfield may indicate the version of the WLAN protocol applied to the corresponding MAC frame.

The Type subfield and the Subtype subfield may be set to indicate information for identifying a function of a corresponding MAC frame.

The type of the MAC frame may include three frame types: a management frame, a control frame, and a data frame.

Each frame type may be further divided into subtypes.

For example, control frames include request to send (RTS) frames, clear-to-send (CTS) frames, acknowledgment (ACK) frames, PS-Poll frames, content free (End) frames, CF End + CF-ACK frame, Block Acknowledgment request (BAR) frame, Block Acknowledgment (BA) frame, Control Wrapper (Control + HTcontrol) frame, VHT null data packet notification (NDPA) It may include a Null Data Packet Announcement and a Beamforming Report Poll frame.

Management frames include beacon frames, announcement traffic indication message (ATIM) frames, disassociation frames, association request / response frames, reassociation requests / responses Response frame, Probe Request / Response frame, Authentication frame, Deauthentication frame, Action frame, Action No ACK frame, Timing Advertisement It may include a frame.

The To DS subfield and the From DS subfield may include information necessary to interpret the Address 1 field or the Address 4 field included in the corresponding MAC frame header. In the case of a control frame, both the To DS subfield and the From DS subfield are set to '0'. For a Management frame, the To DS subfield and the From DS subfield are set to '1' and '0' in order if the frame is a QoS Management frame (QMF), and in order if the frame is not QMF. Both can be set to '0', '0'.

The More Fragments subfield may indicate whether there is a fragment to be transmitted following the corresponding MAC frame. If there is another fragment of the current MSDU or MMPDU, it may be set to '1', otherwise it may be set to '0'.

The Retry subfield may indicate whether the corresponding MAC frame is due to retransmission of a previous MAC frame. In case of retransmission of the previous MAC frame, it may be set to '1', otherwise it may be set to '0'.

The power management subfield may indicate a power management mode of the STA. If the value of the Power Management subfield is '1', the STA may indicate switching to the power save mode.

The More Data subfield may indicate whether there is an additional MAC frame to be transmitted. If there is an additional MAC frame to be transmitted, it may be set to '1', otherwise it may be set to '0'.

The Protected Frame subfield may indicate whether the frame body field is encrypted. If the Frame Body field includes information processed by the encryption encapsulation algorithm, it may be set to '1', otherwise it may be set to '0'.

Information included in each field described above may follow the definition of the IEEE 802.11 system. In addition, each field described above corresponds to an example of fields that may be included in the MAC frame, but is not limited thereto. That is, each field described above may be replaced with another field or additional fields may be further included, and all fields may not be necessarily included.

8 illustrates the VHT format of the HT Control field in a wireless communication system to which the present invention can be applied.

Referring to FIG. 8, the HT Control field includes a VHT subfield, an HT Control Middle subfield, an AC Constraint subfield, and a Reverse Direction Grant (RDG) / More PPDU (More PPDU). It may consist of subfields.

The VHT subfield indicates whether the HT Control field has the format of the HT Control field for the VHT (VHT = 1) or has the format of the HT Control field for the HT (VHT = 0). In FIG. 8, it is assumed that the HT Control field (that is, VHT = 1) for VHT. The HT Control field for the VHT may be referred to as a VHT Control field.

The HT Control Middle subfield may be implemented to have a different format according to the indication of the VHT subfield. A more detailed description of the HT Control Middle subfield will be given later.

The AC Constraint subfield indicates whether a mapped AC (Access Category) of a reverse direction (RD) data frame is limited to a single AC.

The RDG / More PPDU subfield may be interpreted differently depending on whether the corresponding field is transmitted by the RD initiator or the RD responder.

When transmitted by the RD initiator, the RDG / More PPDU field is set to '1' if the RDG exists, and set to '0' if the RDG does not exist. When transmitted by the RD responder, it is set to '1' if the PPDU including the corresponding subfield is the last frame transmitted by the RD responder, and set to '0' when another PPDU is transmitted.

As described above, the HT Control Middle subfield may be implemented to have a different format according to the indication of the VHT subfield.

The HT Control Middle subfield of the HT Control field for VHT includes a reserved bit, a Modulation and Coding Scheme feedback request (MRQ) subfield, and an MRQ Sequence Identifier (MSI). Space-time block coding (STBC) subfield, MCS feedback sequence identifier (MFSI) / Least Significant Bit (LSB) of Group ID (LSB) subfield, MCS Feedback (MFB) Subfield, Group ID Most Significant Bit (MSB) of Group ID (MSB) Subfield, Coding Type Subfield, Feedback Transmission Type (FB Tx Type: Feedback transmission type) subfield and a voluntary MFB (Unsolicited MFB) subfield.

In addition, the MFB subfield may include a VHT number of space time streams (NUM_STS) subfield, a VHT-MCS subfield, a bandwidth (BW) subfield, and a signal to noise ratio (SNR). It may include subfields.

The NUM_STS subfield indicates the number of recommended spatial streams. The VHT-MCS subfield indicates a recommended MCS. The BW subfield indicates bandwidth information related to the recommended MCS. The SNR subfield indicates the average SNR value on the data subcarrier and spatial stream.

Information included in each field described above may follow the definition of the IEEE 802.11 system. In addition, each field described above corresponds to an example of fields that may be included in the MAC frame, but is not limited thereto. That is, each field described above may be replaced with another field or additional fields may be further included, and all fields may not be necessarily included.

Media access mechanism

In IEEE 802.11, communication is fundamentally different from the wired channel environment because the communication takes place over a shared wireless medium.

In a wired channel environment, communication is possible based on carrier sense multiple access / collision detection (CSMA / CD). For example, once a signal is transmitted from the transmitter, the channel environment does not change so much that the receiver does not experience significant signal attenuation. At this time, if two or more signals collided, detection was possible. This is because the power sensed by the receiver is instantaneously greater than the power transmitted by the transmitter. However, in a wireless channel environment, a variety of factors (e.g., large attenuation of the signal depending on distance, or instantaneous deep fading) can affect the channel so that the signal actually transmits properly at the receiving end. Whether this has occurred or a collision has occurred, the transmitter cannot accurately perform carrier sensing.

Accordingly, in a WLAN system according to IEEE 802.11, a carrier sense multiple access with collision avoidance (CSMA / CA) mechanism is introduced as a basic access mechanism of a MAC. The CAMA / 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 interval (eg, DCF Inter-Frame Space (DIFS)) prior to starting transmission. Perform Clear Channel Assessment (CCA) sensing. As a result of sensing, if it is determined that the medium is in an idle state, the frame transmission is started through the medium. On the other hand, if the medium is detected to be occupied status, the AP and / or STA does not start its own transmission and assumes that several STAs are already waiting to use the medium. The frame transmission may be attempted after waiting longer for a delay time (eg, a random backoff period) for access.

By applying a random backoff period, assuming that there are several STAs for transmitting a frame, the STAs are expected to have different backoff period values, so that they will wait for different times before attempting frame transmission. This can minimize collisions.

In addition, the IEEE 802.11 MAC protocol provides a hybrid coordination function (HCF). HCF is based on the DCF and 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 a large number of users, and HCCA is 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).

9 is a diagram for explaining an arbitrary backoff period and a frame transmission procedure in a wireless communication system to which the present invention can be applied.

When a certain medium changes from occupy or busy to idle, several STAs may attempt to transmit data (or frames). At this time, as a method for minimizing the collision, STAs may select a random backoff count and wait for a slot time corresponding thereto to attempt transmission. The random backoff count has a pseudo-random integer value and may be determined as one of values uniformly distributed in the range of 0 to a contention window (CW). Where CW is a contention window parameter value. The CW parameter is given CW_min as an initial value, but may take a double value when transmission fails (eg, when an ACK for a transmitted frame is not received). If the CW parameter value is CW_max, data transmission can be attempted while maintaining the CW_max value until the data transmission is successful. If the CW parameter value is successful, the CW parameter value is reset to the CW_min value. The CW, CW_min and CW_max values are preferably set to (2 ^ n) -1 (n = 0, 1, 2, ...).

When the random backoff process begins, the STA counts down the backoff slot according to the determined backoff count value and continuously monitors the medium during the countdown. If the media is monitored as occupied, the countdown stops and waits, and when the media is idle the countdown resumes.

In the example of FIG. 9, when a packet to be transmitted to the MAC of the STA 3 arrives, the STA 3 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 be transmitted in each of STA 1, STA 2, and STA 5, and each STA waits for DIFS when the medium is monitored in an idle state, and then backoff slots according to a random backoff count value selected by each STA. Counts down.

In the example of FIG. 9, STA 2 selects the smallest backoff count value and STA 1 selects the largest backoff count value. That is, at the time when STA 2 finishes the backoff count and starts frame transmission, the remaining backoff time of STA 5 is shorter than the remaining backoff time of STA 1.

STA 1 and STA 5 stop counting and wait while STA 2 occupies the medium. When the media occupancy of the STA 2 ends and the medium becomes idle again, the STA 1 and the STA 5 resume 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 STA 5 is shorter than that of STA 1, frame transmission of STA 5 is started.

Meanwhile, while STA 2 occupies the medium, data to be transmitted may also occur in STA 4. At this time, when the medium is in the idle state, the STA 4 waits for DIFS and then counts down the backoff slot according to the random backoff count value selected by the STA.

In the example of FIG. 9, the remaining backoff time of STA 5 coincides with an arbitrary backoff count value of STA 4, and in this case, a collision may occur between STA 4 and STA 5. If a collision occurs, neither STA 4 nor STA 5 receive an ACK, and thus data transmission fails. In this case, STA4 and STA5 select a random backoff count value after doubling the CW value and perform countdown of the backoff slot.

Meanwhile, the STA 1 may wait while the medium is occupied due to the transmission of the STA 4 and the STA 5, wait for DIFS when the medium is idle, and then start frame transmission after the remaining backoff time passes.

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

Virtual carrier sensing is intended to compensate for problems that may occur in media access, such as a hidden node problem. For virtual carrier sensing, the MAC of the WLAN system uses a Network Allocation Vector (NAV). The NAV is a value that indicates to the other AP and / or STA how long the AP and / or STA currently using or authorized to use the medium remain until the medium becomes available. Therefore, the value set to NAV corresponds to a period in which the medium is scheduled to be used by the AP and / or STA transmitting the frame, and the STA receiving the NAV value is prohibited from accessing the medium during the period. For example, the NAV may be set according to a value of a duration field of the MAC header of the frame.

The AP and / or STA may perform a procedure of exchanging a request to send (RTS) frame and a clear to send (CTS) frame to indicate that the AP and / or STA want to access the medium. The RTS frame and the CTS frame include information indicating a time interval in which a wireless medium required for transmission and reception of an ACK frame is reserved when substantial data frame transmission and acknowledgment (ACK) are supported. The other STA that receives the RTS frame transmitted from the AP and / or the STA to which the frame is to be transmitted or receives the CTS frame transmitted from the STA to which the frame is to be transmitted during the time period indicated by the information included in the RTS / CTS frame Can be set to not access the medium. This may be implemented by setting the NAV during the time interval.

Frame spacing ( interframe  space)

The time interval between frames is defined as Interframe Space (IFS). The STA may determine whether the channel is used during the IFS time interval through carrier sensing. Multiple IFSs are defined to provide a priority level that occupies a wireless medium in an 802.11 WLAN system.

10 is a diagram illustrating an IFS relationship in a wireless communication system to which the present invention can be applied.

All timings can be determined with reference to the physical layer interface primitives, namely the PHY-TXEND.confirm primitive, the PHYTXSTART.confirm primitive, the PHY-RXSTART.indication primitive and the PHY-RXEND.indication primitive.

Frame spacing according to IFS type is as follows.

a) reduced interframe space (RIFS)

b) short interframe space (SIFS)

c) PCF frame interval (PIFS: PCF interframe space)

d) DCF frame interval (DIFS: DCF interframe space)

e) arbitration interframe space (AIFS)

f) extended interframe space (EIFS)

Different IFSs are determined from attributes specified by the physical layer regardless of the bit rate of the STA. IFS timing is defined as the time gap on the medium. Except for AIFS, IFS timing is fixed for each physical layer.

SIFS is a PPDU containing a ACK frame, a CTS frame, a Block ACK Request (BlockAckReq) frame, or a Block ACK (BlockAck) frame that is an immediate response to an A-MPDU, the second or consecutive MPDU of a fragment burst, or PCF. Used for transmission of the STA's response to polling by and has the highest priority. SIFS can also be used for point coordinator of frames regardless of the type of frame during non-competition interval (CFP) time. SIFS represents the time from the end of the last symbol of the previous frame or the signal extension (if present) to the start of the first symbol of the preamble of the next frame.

SIFS timing is achieved when the transmission of consecutive frames at the TxSIFS slot boundary begins.

SIFS is the shortest of the IFS between transmissions from different STAs. The STA occupying the medium may be used when it is necessary to maintain the occupation of the medium during the period in which the frame exchange sequence is performed.

By using the smallest gap between transmissions in the frame exchange sequence, it is possible to prevent other STAs that are required to wait for the medium to idle for a longer gap to attempt to use the medium. Thus, priority can be given to the completion of an ongoing frame exchange sequence.

PIFS is used to gain priority in accessing media.

PIFS can be used in the following cases:

STAs operating under PCF

STA that transmits a Channel Switch Announcement frame

STA that transmits a Traffic Indication Map (TIM) frame

Hybrid Coordinator (HC) initiating CFP or Transmission Opportunity (TXOP)

HC or non-AP QoS STA, which is a polled TXOP holder for recovering from the absence of expected reception in a controlled access phase (CAP)

-HT STA using dual CTS protection before transmission of CTS2

TXOP holder for continuing transmission after a transmission failure

Reverse direction (RD) initiator to continue transmission using error recovery

HT AP during PSMP sequence transmitting power save multi-poll (PSMP) recovery frames

HT STA performing CCA in a secondary channel before transmitting a 40 MHz mask PPDU using EDCA channel access

Except in the case of performing the CCA in the secondary channel (secondary channel) of the examples listed above, the STA using the PIFS starts transmission after the CS (carrier sense) mechanism that determines that the medium is idle at the TxPIFS slot boundary.

DIFS may be used by a STA operative to transmit a data frame (MPDU) and a management frame (MMPDU: MAC Management Protocol Data Unit) under DCF. The STA using the DCF may transmit on the TxDIFS slot boundary if it is determined that the medium is idle through a carrier sense (CS) mechanism after a correctly received frame and backoff time expire. Here, the correctly received frame means a frame in which the PHY-RXEND.indication primitive does not indicate an error and the FCS indicates that the frame is not an error (error free).

SIFS time 'aSIFSTime' and slot time 'aSlotTime' may be determined for each physical layer. The SIFS time has a fixed value, but the slot time may change dynamically according to a change in the air delay time (aAirPropagationTime).

Block Ack Procedure

11 is a diagram illustrating a downlink MU-MIMO transmission process in a wireless communication system to which the present invention can be applied.

In 802.11ac, MU-MIMO is defined in downlink from the AP to the client (ie, non-AP STA). In this case, a multi-user frame is simultaneously transmitted to multiple receivers, but acknowledgments should be transmitted separately in the uplink.

Since all MPDUs transmitted in the VHT MU PPDU based on 802.11ac are included in the A-MPDU, the response to the A-MPDU in the VHT MU PPDU, rather than the immediate response to the VHT MU PPDU, is a block ACK request by the AP (BAR). : Block Ack Request) is sent in response to a frame.

First, the AP transmits a VHT MU PPDU (ie, preamble and data) to all receivers (ie, STA 1, STA 2, and STA 3). The VHT MU PPDU includes a VHT A-MPDU transmitted to each STA.

Receiving a VHT MU PPDU from the AP, STA 1 transmits a block acknowledgment (BA) frame to the AP after SIFS. The BA frame will be described later in more detail.

After receiving the BA from the STA 1, the AP transmits a block acknowledgment request (BAR) frame to the next STA 2 after SIFS, and the STA 2 transmits a BA frame to the AP after SIFS. The AP receiving the BA frame from STA 2 transmits the BAR frame to STA 3 after SIFS, and STA 3 transmits the BA frame to AP after SIFS.

If this process is performed for all STAs, the AP transmits the next MU PPDU to all STAs.

HE (High Efficiency, 802. 11ax ) system

Hereinafter, a next generation WLAN system will be described. The next generation WLAN system is a next generation WIFI system, which may be described as an example of IEEE 802.11ax as an embodiment of the next generation WIFI system. In the present specification, the following next-generation WLAN systems are referred to as HE (High Efficiency) systems, and frames, PPDUs, and the like of the system are referred to as HE frames, HE PPDUs, HE preambles, HE-SIG fields, HE-STFs, and HE-LTFs. May be referred to.

The description of the existing WLAN system such as the above-described VHT system may be applied to the HE system, which is not further described below. For example, for the VHT-SIG A field, VHT-STF, VHT-LTF and VHT-SIG-B fields described above for the HE-SIG A field, HE-STF, HE-LTF and HE-SIG-B fields. Description may apply. The HE frame and the preamble of the proposed HE system may be used only for other wireless communication or cellular systems. The HE STA may be a non-AP STA or an AP STA as described above. Although referred to as STA in the following specification, such a STA device may represent an HE STA device.

12 illustrates a High Efficiency (HE) format PPDU according to an embodiment of the present invention.

12 (a) illustrates a schematic structure of the HE format PPDU, and FIGS. 12 (b) to (d) illustrate a more specific structure of the HE format PPDU.

Referring to FIG. 12A, a HE format PPDU for an HEW may be largely composed of a legacy part (L-part), an HE part (HE-part), and a data field (HE-data).

The L-part is composed of an L-STF field, an L-LTF field, and an L-SIG field in the same manner as the conventional WLAN system maintains. The L-STF field, L-LTF field, and L-SIG field may be referred to as a legacy preamble.

The HE-part is a part newly defined for the 802.11ax standard and may include an HE-STF field, an HE-SIG field, and an HE-LTF field. 12 (a) illustrates the order of the HE-STF field, the HE-SIG field, and the HE-LTF field, but may be configured in a different order. In addition, HE-LTF may be omitted. In addition to the HE-STF field and the HE-LTF field, the HE-SIG field may be collectively referred to as HE-preamble.

In addition, the L-part, the HE-SIG field, and the HE-preamble may be collectively referred to as a physical preamble (PHY) / physical preamble.

The HE-SIG field may include information (eg, OFDMA, UL MU MIMO, enhanced MCS, etc.) for decoding the HE-data field.

The L-part and the HE-part may have different fast fourier transform (FFT) sizes (ie, subcarrier spacing), and may use different cyclic prefixes (CP).

802.11ax systems can use FFT sizes that are four times larger than legacy WLAN systems. That is, the L-part may have a 1 × symbol structure, and the HE-part (particularly, HE-preamble and HE-data) may have a 4 × symbol structure. Here, 1 ×, 2 ×, 4 × size FFTs represent relative sizes for legacy WLAN systems (eg, IEEE 802.11a, 802.11n, 802.11ac, etc.).

For example, if the FFT size used for the L-part is 64, 128, 256, and 512 at 20 MHz, 40 MHz, 80 MHz, and 200 MHz, respectively, the FFT size used for the HE-part is 256 at 20 MHz, 40 MHz, 80 MHz, and 200 MHz, respectively. , 512, 1024, 2048.

As the FFT size becomes larger than the legacy WLAN system, the number of subcarriers per unit frequency increases because the subcarrier frequency spacing becomes smaller, but the OFDM symbol length becomes longer.

That is, the use of a larger FFT size means that the subcarrier spacing becomes narrower, and similarly, an Inverse Discrete Fourier Transform (IDFT) / Discrete Fourier Transform (DFT) period is increased. Here, the IDFT / DFT period may mean a symbol length excluding the guard period (GI) in the OFDM symbol.

Therefore, if the HE-part (particularly HE-preamble and HE-data) is used with an FFT size four times larger than the L-part, the subcarrier spacing of the HE-part is 1/4 of the subcarrier spacing of the L-part. The ID-FT / DFT period of the HE-part is four times the IDFT / DFT period of the L-part. For example, if the subcarrier spacing of L-part is 312.5kHz (= 20MHz / 64, 40MHZ / 128, 80MHz / 256 and / or 200MHz / 512), the subcarrier spacing of HE-part is 78.125kHz (= 20MHz / 256 , 40MHZ / 512, 80MHz / 1024 and / or 200MHz / 2048). Also, if the IDFT / DFT period of the L-part is 3.2 ms (= 1 / 312.5 kHz), the IDFT / DFT period of the HE-part may be 12.8 ms (= 1 / 78.125 kHz).

Here, the GI can be one of 0.8 ㎲, 1.6 ㎲, 3.2 ㎲, so the OFDM symbol length (or symbol interval) of the HE-part including the GI is 13.6 ㎲, 14.4 ㎲, 20 according to the GI. It can be

Referring to FIG. 12B, the HE-SIG field may be divided into an HE-SIG-A field and an HE-SIG-B field.

For example, the HE-part of the HE format PPDU may include a HE-SIG-A field having a length of 12.8 kHz, a HE-STF field of 1 OFDM symbol, one or more HE-LTF fields, and a HE-SIG-B field of 1 OFDM symbol. It may include.

In addition, in the HE-part, except for the HE-SIG-A field, the FFT having a size four times larger than the existing PPDU may be applied from the HE-STF field. That is, FFTs of 256, 512, 1024, and 2048 sizes may be applied from the HE-STF field of the HE format PPDU of 20 MHz, 40 MHz, 80 MHz, and 200 MHz, respectively.

However, when the HE-SIG is divided into the HE-SIG-A field and the HE-SIG-B field and transmitted as shown in FIG. 12 (b), the positions of the HE-SIG-A field and the HE-SIG-B field are shown in FIG. It may differ from 12 (b). For example, the HE-SIG-B field may be transmitted after the HE-SIG-A field, and the HE-STF field and the HE-LTF field may be transmitted after the HE-SIG-B field. In this case, an FFT of 4 times larger than a conventional PPDU may be applied from the HE-STF field.

Referring to FIG. 12C, the HE-SIG field may not be divided into an HE-SIG-A field and an HE-SIG-B field.

For example, the HE-part of the HE format PPDU may include a HE-STF field of one OFDM symbol, a HE-SIG field of one OFDM symbol, and one or more HE-LTF fields.

Similar to the above, the HE-part may be applied to an FFT four times larger than the existing PPDU. That is, FFTs of 256, 512, 1024, and 2048 sizes may be applied from the HE-STF field of the HE format PPDU of 20 MHz, 40 MHz, 80 MHz, and 200 MHz, respectively.

Referring to FIG. 12 (d), the HE-SIG field is not divided into an HE-SIG-A field and an HE-SIG-B field, and the HE-LTF field may be omitted.

For example, the HE-part of the HE format PPDU may include a HE-STF field of 1 OFDM symbol and a HE-SIG field of 1 OFDM symbol.

Similar to the above, the HE-part may be applied to an FFT four times larger than the existing PPDU. That is, FFTs of 256, 512, 1024, and 2048 sizes may be applied from the HE-STF field of the HE format PPDU of 20 MHz, 40 MHz, 80 MHz, and 200 MHz, respectively.

The HE format PPDU for the WLAN system according to the present invention may be transmitted on at least one 20 MHz channel. For example, an HE format PPDU can be transmitted in a 40 MHz, 80 MHz or 200 MHz frequency band using a total of four 20 MHz channels. This will be described in more detail with reference to the drawings below.

13 is a diagram illustrating an HE format PPDU according to an embodiment of the present invention.

FIG. 13 illustrates a PPDU format when 80 MHz is allocated to one STA (or OFDMA resource units are allocated to a plurality of STAs within 80 MHz) or when different streams of 80 MHz are allocated to a plurality of STAs.

Referring to FIG. 13, L-STF, L-LTF, and L-SIG may be transmitted as OFDM symbols generated based on 64 FFT points (or 64 subcarriers) in each 20MHz channel.

The HE-SIG-A field may include common control information that is commonly transmitted to STAs receiving a PPDU. The HE-SIG-A field may be transmitted in one to three OFDM symbols. The HE-SIG-A field is copied in units of 20 MHz and contains the same information. In addition, the HE-SIG-A field informs the total bandwidth information of the system.

The HE-SIG-A field may include information as shown in Table 1 below.

Information included in each field illustrated in Table 1 may follow the definition of the IEEE 802.11 system. In addition, each field described above corresponds to an example of fields that may be included in the PPDU, but is not limited thereto. That is, each field described above may be replaced with another field or additional fields may be further included, and all fields may not be necessarily included.

HE-STF is used to improve the performance of AGC (Automatic Gain Control) estimation in MIMO transmission. HE-STF may be generated using a sequence of frequency domains for a particular band. Long Trainig Field (HE-LTF) is a field used at the receiver to estimate the MIMO channel between the receive chains and the set of constellation mapper outputs.

The HE-SIG-B field may include user-specific information required for each STA to receive its own data (eg, PSDU). The HE-SIG-B field may be transmitted in one or two OFDM symbols. For example, the HE-SIG-B field may include information on the modulation and coding scheme (MCS) of the corresponding PSDU and the length of the corresponding PSDU.

The L-STF, L-LTF, L-SIG, and HE-SIG-A fields may be repeatedly transmitted in units of 20 MHz channels. For example, when a PPDU is transmitted on four 20 MHz channels (i.e., 80 MHz band), the L-STF, L-LTF, L-SIG and HE-SIG-A fields may be repeatedly transmitted on every 20 MHz channel. have.

As the FFT size increases, legacy STAs supporting legacy IEEE 802.11a / g / n / ac may not be able to decode the HE PPDU. In order for the legacy STA and the HE STA to coexist, the L-STF, L-LTF, and L-SIG fields are transmitted through a 64 FFT on a 20 MHz channel so that the legacy STA can receive them. For example, the L-SIG field may occupy one OFDM symbol, one OFDM symbol time is 4 ms, and a GI may be 0.8 ms.

The FFT size for each frequency unit may be larger from the HE-STF (or HE-SIG-A). For example, 256 FFTs may be used in a 20 MHz channel, 512 FFTs may be used in a 40 MHz channel, and 1024 FFTs may be used in an 80 MHz channel. As the FFT size increases, the number of OFDM subcarriers per unit frequency increases because the interval between OFDM subcarriers becomes smaller, but the OFDM symbol time becomes longer. In order to improve the efficiency of the system, the length of the GI after the HE-STF may be set equal to the length of the GI of the HE-SIG-A.

The HE-SIG-A field may include information required for the HE STA to decode the HE PPDU. However, the HE-SIG-A field may be transmitted through a 64 FFT in a 20 MHz channel so that both the legacy STA and the HE STA can receive it. This is because the HE STA can receive not only the HE format PPDU but also the existing HT / VHT format PPDU, and the legacy STA and the HE STA must distinguish between the HT / VHT format PPDU and the HE format PPDU.

14 is a diagram illustrating an HE format PPDU according to an embodiment of the present invention.

In FIG. 14, it is assumed that 20 MHz channels are allocated to different STAs (eg, STA 1, STA 2, STA 3, and STA 4).

Referring to FIG. 14, the FFT size per unit frequency may be larger from the HE-STF (or HE-SIG-B). For example, from the HE-STF (or HE-SIG-B), 256 FFTs may be used in a 20 MHz channel, 512 FFTs may be used in a 40 MHz channel, and 1024 FFTs may be used in an 80 MHz channel.

Since the information transmitted in each field included in the PPDU is the same as the example of FIG. 13, a description thereof will be omitted.

The HE-SIG-B field may include information specific to each STA, but may be encoded over the entire band (ie, indicated by the HE-SIG-A field). That is, the HE-SIG-B field includes information on all STAs and may be transmitted so that all STAs receive.

The HE-SIG-B field may inform frequency bandwidth information allocated to each STA and / or stream information in a corresponding frequency band. For example, in FIG. 14, the HE-SIG-B may be allocated 20 MHz for STA 1, 20 MHz for STA 2, 20 MHz for STA 3, and 20 MHz for STA 4. In addition, STA 1 and STA 2 may allocate 40 MHz, and STA 3 and STA 4 may then allocate 40 MHz. In this case, STA 1 and STA 2 may allocate different streams, and STA 3 and STA 4 may allocate different streams.

In addition, by defining the HE-SIG-C field, the HE-SIG C field may be added to the example of FIG. 14. In this case, in the HE-SIG-B field, information on all STAs may be transmitted over the entire band, and control information specific to each STA may be transmitted in units of 20 MHz through the HE-SIG-C field. In this case, the HE-SIG-C field may be transmitted after the HE-LTF field.

In addition, unlike the examples of FIGS. 13 and 14, the HE-SIG-B field may be transmitted in units of 20 MHz in the same manner as the HE-SIG-A field without transmitting over the entire band. This will be described with reference to the drawings below.

15 is a diagram illustrating a HE format PPDU according to an embodiment of the present invention.

In FIG. 15, it is assumed that 20 MHz channels are allocated to different STAs (eg, STA 1, STA 2, STA 3, and STA 4).

Referring to FIG. 15, the HE-SIG-B field is not transmitted over the entire band, but is transmitted in 20 MHz units in the same manner as the HE-SIG-A field. However, at this time, the HE-SIG-B is encoded and transmitted in 20 MHz units differently from the HE-SIG-A field, but may not be copied and transmitted in 20 MHz units.

In this case, the FFT size per unit frequency may be larger from the HE-STF (or HE-SIG-B). For example, from the HE-STF (or HE-SIG-B), 256 FFTs may be used in a 20 MHz channel, 512 FFTs may be used in a 40 MHz channel, and 1024 FFTs may be used in an 80 MHz channel.

Since the information transmitted in each field included in the PPDU is the same as the example of FIG. 13, a description thereof will be omitted.

The HE-SIG-A field is duplicated and transmitted in units of 20 MHz.

The HE-SIG-B field may inform frequency bandwidth information allocated to each STA and / or stream information in a corresponding frequency band. Since the HE-SIG-B field includes information about each STA, information about each STA may be included for each HE-SIG-B field in units of 20 MHz. In this case, in the example of FIG. 15, 20 MHz is allocated to each STA. For example, when 40 MHz is allocated to the STA, the HE-SIG-B field may be copied and transmitted in units of 20 MHz.

It may be more preferable not to transmit the HE-SIG-B field over the entire band as in the case of allocating a part of the bandwidth having a low interference level from the adjacent BSS to the STA in a situation in which different bandwidths are supported for each BSS. .

13 to 15, the data field is a payload and may include a service field, a scrambled PSDU, tail bits, and padding bits.

Meanwhile, the HE format PPDU as shown in FIGS. 13 to 15 may be identified through a RL-SIG (Repeated L-SIG) field, which is a repetitive symbol of the L-SIG field. The RL-SIG field is inserted before the HE SIG-A field, and each STA may identify the format of the received PPDU as the HE format PPDU using the RL-SIG field.

HE Of STA CCA  How To

Hereinafter, the CCA method of the HE STA will be described in more detail. As described above, the AP STA and the non-AP STA perform a clear channel assessment (CCA) to determine a busy / idle state of the channel. CCA represents a logical function / operation at the physical layer that determines the current usage state of the wireless medium (WM).

The STA performs CCA in the physical layer and reports the result to the MAC layer. The STA may perform CCA-ED (Energy Detection) and CCA-CS (Carrier sensing) as two modes of CCA. As an embodiment, the STA may determine the occupancy / idle mode of the channel by performing CCA-ED, performing CCA-CS, or using a combination of CCS-CS and CCA-ED. When using a combination of CCS-CS and CCA-ED, the STA may perform CCA by first performing CCA-CS and additionally performing CCA-ED, performing CCA-ED first, and then further CCA-ED. CCA may be performed by performing CS.

The CCA-CS is performed through signal detection for the preamble, and the threshold of the CCA-CS is determined based on the minimum modulation and code rate sensitivity. In addition, the level of the CCA-CS, that is, the threshold value may be set to a different value according to the bandwidth. For example, the STA determines that the channel is busy when the received preamble signal is greater than -82 dBm in the case of 20 MHz channel spacing, and when the magnitude of the received preamble signal is greater than -85 dBm in the case of 10 MHz channel spacing. It may be determined that the channel is busy, and in the case of 5 MHz channel spacing, if the received preamble signal has a magnitude of -88 dBm or more, it may be determined that the channel is busy. As an embodiment, the STA may perform CCA-CS using the correlation of the STF in the preamble of the 802.11a signal. In the present specification, a CCA threshold / threshold value in dBm may be referred to as a CCA level.

In the case of CCA-ED, the STA determines to occupy when any signal is detected with an intensity (dBm) equal to or greater than the threshold value regardless of the signal defined in the 802.11 system. In this case, the threshold can be estimated to be 20dBm higher than the CCA-CS. For example, in case of 20 MHz channel spacing, the STA determines that the channel is occupied if it is -62 dBm or more, and in case of 10 MHz channel spacing, the STA determines that the channel is busy when the magnitude of the received preamble signal is -65 dBm or more, and 5 MHz In the case of channel spacing, if the received preamble signal has a magnitude of -68 dBm or more, it may be determined that the channel is busy.

The method described below may be applied to both CCA-CS and CCA-ED, but the following embodiment will be described as STA performing CCA-CS.

If the STA and system support broadband such as 20/40/80/200 MHz, different CCA levels can be applied between the primary and non-primary channels, in which case each channel bandwidth CCA level (threshold values) according to the can be defined as shown in Table 2.

In Table 2, since there is no secondary channel for the 200 MHz channel, the corresponding signal threshold / energy threshold is not defined.

16 is a conceptual diagram illustrating a method of performing CCA according to an embodiment of the present invention.

As described above, since the CCA level, that is, the CCA threshold is operated at a fixed value within one BSS for each channel bandwidth, efficient resource operation may be difficult in space. In FIG. 16 and the following embodiments, AP1 and STA1 may belong to the first BSS and AP2 and STA2 may belong to the second BSS.

In the embodiment of FIG. 16, AP2 may transmit a PPDU to STA2 through a 20 MHz channel. At this time, if the signal transmitted by AP2 is received to AP1 by more than -82dBm, AP1 determines that the channel is occupied and does not transmit the signal to STA1. However, in an environment where AP1 and STA1 are sufficiently separated from AP2 or STA2, or in an environment in which interference of a signal transmitted by AP1 is not largely affected by STA2, it is more efficient for AP1 to transmit a signal to STA1. In other words, by using a fixed CCA level, space resource usage efficiency is reduced. This may be a problem especially when the BSS to which AP1 and STA1 belong and the BSS to which AP2 and STA2 belong are different, especially when the two BSSs are OBSS.

Therefore, in order to improve spatial efficiency, a method of dynamically adjusting a CCA level according to an STA and determining a occupation / idle state of a channel based on the adjusted CCA level will be proposed and described. Hereinafter, a method of dynamically adjusting the CCA level by the STA will be described in more detail with reference to calculating and adjusting the CCA level and managing the CCA level.

In the following embodiments, the CCA level change may be applied to STAs belonging to different BSSs. In particular, it can be used to increase the spatial reuse efficiency of bandwidth between STAs in OBSS.

As a method for adjusting the CCA level, the present invention proposes a method for determining or adjusting the CCA level using ACK information or block ACK information. As a method of determining / calculating the CCA level using the ACK information, a proactive method and a reactive method are proposed.

ACK information or block ACK information may be referred to as an ACK frame or a block ACK frame. An ACK frame may be transmitted in response to the MPDU, and a block ACK frame may be transmitted in response to the A-MPDU. The ACK frame may include a frame control field, a duration field, an RA field, and an FCS. The ACK frame is a control frame, which is a signal / information transmitted by the STA that has received the data to inform the STA that has transmitted the data well. Hereinafter, the ACK frame may be used to include a block ACK frame, and the number of ACK frames may also be the number of ACK frames including a block ACK frame. (For example, the number of ACK frames and the number of each block ACK frame may be added to indicate the number of ACK frames.)

17 is a conceptual diagram illustrating a method for adjusting CCA levels according to an embodiment of the present invention.

FIG. 17 illustrates a proactive method in which an STA adjusts a CCA level using an ACK or block ACK signal transmitted from a neighboring STA or AP. As illustrated in FIG. 17, when STA1 transmits an ACK frame for AP1, AP2 may also receive this ACK frame. The STA may snoop not only an ACK frame for itself but also an ACK frame for another STA. When receiving the ACK frame, AP2 may change its CCA level if the number of ACK frames received is greater than or equal to a certain number. Because the communication link between the STA1 and the AP1 is robust, even if the AP2 communicates with the STA while the STA1 and the AP1 are transmitting, the influence of the STA1 and the AP1 may not be affected or may be small. Hereinafter, the proactive method will be described in more detail as a CCA level adjustment method considering the ACK frame.

The STA may increase / decrease / maintain the CCA level by N dBm when a signal of another SAT / AP received for a predetermined time includes more or less than a certain number of ACK frames. Here, the specific time may be defined as a specific value of a few us (microseconds) to several s (seconds) as an absolute time. As an embodiment, the specific time may be set to a certain multiple of one of slot time, beacon interval, SIFS, PIFS, DIFS, EIFS or AIFS.

The number of ACK frames received over time for changing the CCA level may be defined as a system parameter. In addition, the number of received ACK frames may be indicated to STAs through beacon signaling at the AP. In the method of signaling the number of ACK frames, the AP may indicate differently for each STA, group-wise using a group ID, or common for each BSS. In case of common indication for each BSS, all APs / STAs in the BSS can use the same value. In addition, an interval in which STAs count the number of ACK frames may also be signaled by the AP to indicate differently for each STA, for each group using a group ID, or for common indication for each BSS.

The method of signaling / defining parameters differently for each STA may be efficiently applied when the transmission power is different depending on the type or capability of the STA. This is because the amount of interference affecting neighboring STAs may vary depending on communication for each STA. As an embodiment, since an STA having a large transmission power has a large influence on the surroundings when transmitting a signal, the AP may set the number of ACK frames that the STA changes CCA level to be larger than the number of ACK frames of other STAs. Signaling / setting can be made. Accordingly, the AP may lower the interference to other STAs by the STA by reducing the increase in the transmission frequency due to the change in the CCA level of the STA having the high transmission power.

The operation of changing the CCA level according to the number of ACK frames by the STA may be performed as follows. As described above, the number of ACK frames may be the number of ACK frames for other STAs counted by the STA or the number of ACK frames received as signaling information.

1) When the number of ACK frames is larger than the first threshold (# of ACK> threshold1)

The CCA level value N to be changed may be any positive integer including zero. The N value may be an integer value corresponding to a dBm unit. As an embodiment, the STA may increase the CCA level by N dB when the number of ACKs is greater than the first threshold (# of ACK> threshold1). The maximum value of the CCA level that is changed when the CCA level is changed may be limited to the threshold value of the CCA-ED for the corresponding bandwidth. That is, referring to the example of Table 2, the CCA level for the 20MHz bandwidth can be increased only up to -62dBm.

2) When the number of ACK frames is less than or equal to the first threshold and greater than the second threshold (threshold1> = # of ACK> threshold2)

If the number of ACK frames is less than or equal to the first threshold and greater than the second threshold, the STA may maintain the current CCA level.

3) If the number of ACK frames is less than or equal to the second threshold (threshold2> = # of ACK)

If the number of ACK frames is less than or equal to the first threshold, the STA may change the CCA level by -N dB. (In other words, the STA may reduce the CCA level by N.) In this case, the minimum value of the changed CCA level is limited to the same CCA level value as the legacy STA. That is, referring to the example in Table 2, the CCA level for the 20 MHz bandwidth is at least -82 dBm, the CCA level for the 40 MHz bandwidth is at least -79 dBm, the CCA level for the 80 MHz bandwidth is at least -76 dBm, and 40 MHz The CCA level for the bandwidth can be reduced by at least -73 dBm.

In order for the STA to count the number of ACK frames, it is necessary to determine whether a signal transmitted for the other STA received corresponds to an ACK frame or a block ACK frame. To this end, as described above, whether the corresponding frame is a control frame / management frame / data frame or an ACK frame / block ACK frame among the control frames must be identified, and the STA can identify this by decoding the MAC header information. The STA must succeed in the CRC for the PSDU to decode the MAC header information. Therefore, the present invention further proposes a method of signaling the ACK / block ACK frame identification information through the physical header so that the STA can distinguish the ACK / block ACK frame faster.

The ACK frame identification information may indicate that the corresponding frame corresponds to an ACK frame or a block ACK frame. The ACK frame identification information may be included in the physical preamble and transmitted. That is, the ACK frame identification information may be included in at least one field of the L-SIG field, the HE-STF, the HE-LTF, and the GE-SIG-A / B / C field. However, the ACK frame identification information may be transmitted in the service field.

As an embodiment, the ACK frame identification information may be signaled as a field / flag of 1 bit. The ACK frame identification information may use the reserved bit of the L-SIG or the service field or may be included as an additional field in the HE preamble. In another embodiment, the ACK frame identification information may be signaled with n bits to indicate an attribute for the frame. In this case, one bit / field / information of n bits of information may be used to indicate the ACK / block ACK frame.

18 is a conceptual diagram illustrating a method for adjusting CCA levels according to another embodiment of the present invention.

FIG. 18 is an embodiment for instructing to adjust a CCA level of neighboring STAs when receiving an ACK frame or a block ACK signal with respect to data transmitted by itself, and illustrates a reactive method. In FIG. 18, AP1 may transmit data to STA1 and receive an ACK frame from STA1. If the number of received ACK frames is greater than or equal to a certain number, the AP1 may determine that the communication channel with the STA1 is robust and transmit an instruction to change the CCA level so that the AP2 may transmit to the STA2. When the CCA level is changed according to the CCA level change instruction, AP2 may transmit data to STA2 when the received power is lower than the changed CCA level. With reference to FIG. 18, the contents to which the description of FIG. 17 is applied are not described repeatedly.

In the reactive method, the STA may operate an internal counter when receiving an ACK frame / block ACK frame for data transmitted by the STA. For example, when the ACK signal is received, the counter value is increased to +1, and when the ACK signal is not received, the counter value is reset to 0. When the counter reaches the preset maximum value, the STA may transmit CCA level control information in the signaling field of the next transmitted PPDU. The CCA level control information may indicate whether the CCA level is changed, whether the CCA level is increased / decreased when the CCA level is changed, and may include a CCA level value of increasing / decreasing.

As described above, the CCA level control information / field may be included in at least one of the preambles of the PPDU, that is, the L-SIG field, the HE-STF, the HE-LTF, and the HE-SIG-A / B / C field. The CCA level control information may be signaled as a flag in an on / off form as 1 bit. In particular, when using a reserved field of the L-SIG field may be signaled by 1 bit.

The CCA level control information instructs the STA to change the CCA level and may additionally indicate a change value of the CCA level. For example, the CCA level control information is transmitted using k bits of the PPDU signaling field, and the STA may be transmitted by increasing the value of the CCA level control information by 1 when the ACK counter reaches the maximum value. For example, when k = 2, the transmission is changed from '00' to '01' and the default value of k bits may be '0' or '00'.

When the STA does not receive the ACK, the STA may adjust the value of the CCA level control information by one step and transmit it. As an embodiment, when the STA fails to receive the ACK for a predetermined number of times, the STA may reduce the value of the CCA level control information by one and transmit it.

Upon receiving a signal for another STA, the STA may adjust / receive the CCA level by receiving / decoding the CCA level information included in the preamble. In this case, the maximum value of the CCA level may be limited to the threshold of the CCA-ED for the corresponding bandwidth, and the minimum value of the CCA level may be limited to the CCA level value of the legacy STA. The increase / decrease amount of the CCA level may be expressed as N dB * [value of CCA level control information], and N may be any natural number including zero.

19 is a conceptual diagram illustrating a method for adjusting CCA levels according to another embodiment of the present invention.

In FIG. 19, AP1 and STA1 may be included in the first BSS, AP2 and STA2 may be included in the second BSS, and in particular, it is assumed that STA1 is located at a cell edge of the first BSS. Since STA1 is located at the edge of the first BSS and the communication link with AP1 is not robust, when AP2 transmits data to STA2 using the above-described methods, this signal acts as a co-channel interference (CCI) to STA1. It can greatly affect the communication performance of STA1. In other words, since the STA1 is located at the cell edge and is already receiving data at the lowest MCS due to a poor channel condition, a link failure may occur due to interference due to communication of the STA2.

As described above, when the CCA level is adjusted based only on the number of reception of the ACK frame through the method of FIGS. 17 to 18, the margin for interference of the STA of the neighbor BSS, which is not well channeled, may not be considered. In addition, there is an ambiguity as to which STA the signaling information of AP2 refers to in order to consider the CCA level. This is because there are a plurality of terminals around AP2, and since the channel states of the corresponding terminals are different, the setting of the SIG field may also be different.

In order to solve the above problem, the present invention further proposes a method of measuring RSSI (Receive Signal Strength Indicater) using a signal transmitted from an adjacent AT / STA, and adjusting the CCA level using the acquired RSSI information. do. In addition to RSSI, receiving parameters such as Received Channel Power Indicator (RCPI) or Signal Quailty (SQ) may be used instead of or in conjunction with RSSI. The RSSI parameter is measured at the physical layer as the energy observed at the antenna used to receive the current PPDU. The RSSI may be measured during receiving the physical preamble.

As an embodiment, the STA may measure the strength of signals transmitted and received by other APs / STAs, and may not change the CCA level when the measured signal strength is greater than or equal to a predetermined value, and increase the CCA level when less than or equal to the predetermined value. . This is because, when the measured signal strength is strong, the distance from the corresponding STA is close, and when the measured signal strength is weak, the distance from the corresponding STA may be far. By measuring and using the strength of the received signal, the STA can dynamically operate its CCA level to minimize the interference to neighboring STAs while improving the spatial reuse efficiency of the frequency.

In the example of FIG. 19, a method of adjusting CCA levels when using RSSI is as follows. AP2 may receive the physical preamble of the signal transmitted by STA1, measure signal strength, and calculate RSSI. If the calculated RSSI parameter / value is greater than the third threshold value (RSSI> threshold3), AP2 maintains the CCA level, and if it is less than or equal to the third threshold value (RSSI = <threshold3), AP2 will NCCm the CCA level. Can be increased by Therefore, degradation of communication performance of STA1 due to adjustment of the CCA level of AP2 may be minimized.

As an embodiment, when the AP determines that the STAs of the BSS are well deployed, RSSI measurement for dynamically adjusting the CCA level may be limited to a non-AP STA and an environment at the cell edge. Also, since it is limited to the STA, the complexity for calculating the RSSI can be reduced.

In addition, as an embodiment of the present invention, the STA may use a method of using the aforementioned counter of the ACK frame and a method of using the RSSI.

First, the STA uses the above-described method for adjusting the CCA level based on the ACK frame counting, but can adjust the CCA level only when the RSSI is less than or equal to a specific value. That is, while using the above-described proactive / reactive method, the CCA level is adjusted only when the RSSI value measured in the received signal is less than or equal to the third threshold, and the basic CCA level value is greater when the RSSI value is larger than the third threshold. Can be maintained. As an embodiment, the STA may increase the CCA level when the RSSI value is below the threshold and decrease the CCA level when the RSSI value is above the threshold while using the above-described proactive / reactive method.

Alternatively, the STA may determine the final CCA level increase and decrease by considering both the CCA level increase and decrease according to the ACK-based method and the CCA level increase and decrease according to the RSSI-based method, and control the CCA level accordingly. For example, determine the final CCA level increase or decrease, such as a * (CCA level increase and decrease calculated according to the ACK based method) + b * (CCA level increase and decrease calculated according to the RSSI based method) = final CCA level increase and decrease. Can be. a and b are arbitrary constants and may be differently determined according to the channel condition of the STA.

The above-described methods have been described for STAs in an environment in which transmission (Tx) power is fixed. However, when the transmission power can be controlled, the space efficiency can be further improved by performing the dynamic CCA and controlling the transmission power in parallel. For example, when using the above-described methods, each threshold can be expressed as a function of transmit power (e.g., threshold = function {Tx power (dBm)}, thereby allowing the threshold value to be fluid to the transmit power). Can be assigned to determine a more optimized CCA level.

20 illustrates a STA apparatus according to an embodiment of the present invention.

In FIG. 20, the STA apparatus may include a memory 20010, a processor 20020, and an RF unit 20030. As described above, the STA device may be an AP or a non-AP STA as an HE STA device.

The RF unit 20030 may be connected to the processor 20020 to transmit / receive a radio signal. The RF unit 20030 may upconvert data received from the processor into a transmission / reception band to transmit a signal.

The processor 20020 may be connected to the RF unit 20030 to implement a physical layer and / or a MAC layer according to the IEEE 802.11 system. The processor 20030 may be configured to perform an operation according to various embodiments of the present disclosure according to the above-described drawings and descriptions. In addition, the module for implementing the operation of the STA according to various embodiments of the present invention described above may be stored in the memory 20010 and executed by the processor 20020.

The memory 20010 is connected to the processor 20020 and stores various information for driving the processor 20020. The memory 20010 may be included in the processor 20020 or may be installed outside the processor 20020 and connected to the processor 20020 by known means.

In addition, the STA apparatus may include a single antenna or multiple antennas. The specific configuration of the STA apparatus of FIG. 20 may be implemented so that the matters described in the above-described various embodiments of the present invention are applied independently or two or more embodiments are simultaneously applied.

The CCA adjustment / execution method and the data transmission method of the STA apparatus illustrated in FIG. 20 will be described again with the following flowchart.

21 illustrates a data transmission method of an STA apparatus according to an embodiment of the present invention.

FIG. 21 is a flowchart illustrating a method of adjusting the CCA level using the number of ACK frames, in particular the method of combining the above-described proactive method and the proactive method and the RSSI using method. Although not all mentioned in FIG. 21, the CCA level adjusting method of FIG. 21 may be performed by each of the methods described with reference to FIGS. 16 to 19 or a combination thereof.

The STA may receive a signal for another STA (S21010). As an embodiment, the other STA may be a STA belonging to another BSS or belonging to an OBSS.

If the received signal is an ACK frame signal (S21020), the STA may count the number of ACK frames (S21030). That is, the STA counts the number of ACK frames when the received signal includes the ACK frame, and as described above, the ACK frame may include a block ACK frame. An embodiment of counting the number of ACK frames is as described above.

The STA may decode the MAC header to determine whether the received signal is an ACK frame. In addition, in an embodiment, when the physical preamble of the received signal includes ACK frame identification information indicating whether the received signal is an ACK frame, the STA decodes the ACK frame identification information of the preamble to determine whether the received signal includes the ACK frame. Can be.

The STA may adjust the CCA level according to the number of ACK frames counted during a specific time (S21040). As in the above embodiment, the STA may increase the CCA level when the number of ACK frames is greater than or equal to a certain number (first threshold), and decrease the CCA level when the number of ACK frames is less than or equal to a certain number (second threshold). Can be. The method of adjusting the CCA level according to the number of ACK frames may be performed as described above in the specification.

The STA may perform CCA based on the adjusted CCA level (S21050). When the received signal strength is higher than the adjusted CCA level as a result of performing the CCA, the STA detects the wireless medium as the occupied condition, and if the received signal strength is lower than the adjusted CCA level, the STA detects the corresponding wireless medium as the late condition Can be. And if the wireless medium is in an idle condition, the STA can initiate data transmission. Here, the start of the data transmission may further include the steps of transmitting the RTS frame as well as simply transmitting the data, receiving the CTS frame and transmitting the data as described above.

Although not shown in FIG. 21, the STA may acquire received signal strength information using the received signal and adjust the CCA level based on the received received signal strength information as described above. The received signal strength information may correspond to an RSSI parameter.

The STA may use the RSSI parameter in addition to adjusting the CCA level according to the number of ACK frames, and may determine the CCA level to be adjusted using the RSSI parameter along with the CCA level adjustment according to the number of ACK frames. The STA may maintain the CCA level if the RSSI parameter acquired from the received signal for another STA is greater than the third threshold, and increase the CCA level if the RSSI parameter is greater than or equal to the threshold.

22 illustrates a data transmission method of an STA apparatus according to an embodiment of the present invention.

FIG. 22 is a flowchart illustrating a method for adjusting the CCA level using the number of ACK frames, in particular, a method of combining the above-described reactive method, the reactive method, and the RSSI usage method. Although not all mentioned in FIG. 22, the CCA level adjusting method of FIG. 22 may be performed by each of the methods described in FIGS. 16 to 19 or a combination thereof.

The STA may receive a signal for the STA (S22010).

If the received signal is an ACK frame signal (S22020), the STA may count the number of ACK frames (S22030). That is, the STA counts the number of ACK frames when the received signal includes the ACK frame, and as described above, the ACK frame may include a block ACK frame. An embodiment of counting the number of ACK frames is as described above.

The STA may decode the MAC header to determine whether the received signal is an ACK frame. In addition, in an embodiment, when the physical preamble of the received signal includes ACK frame identification information indicating whether the received signal is an ACK frame, the STA decodes the ACK frame identification information of the preamble to determine whether the received signal includes the ACK frame. Can be.

The STA may transmit a CCA level control signal for adjusting the CCA level of another STA according to the number of ACK frames counted for a specific time (S22040). As in the above-described embodiment, the STA increases the CCA level when the number of ACK frames is greater than or equal to a certain number (first threshold), and decreases the CCA level when the number of ACK frames is less than or equal to a certain number (second threshold). Control signals can be sent. The method of adjusting the CCA level according to the number of frames of the STA that has received the CCA level control signal may be performed as described above in the specification.

Although not shown in FIG. 22, the STA may acquire received signal strength information using the received signal as described above, and may generate and transmit a control signal with a CCA level based on the received received signal strength information. The received signal strength information may correspond to an RSSI parameter.

The STA may use the RSSI parameter in addition to adjusting the CCA level according to the number of ACK frames, and may determine the CCA level to be adjusted using the RSSI parameter along with the CCA level adjustment according to the number of ACK frames. The STA may maintain the CCA level if the RSSI parameter acquired from the received signal for another STA is greater than the third threshold, and increase the CCA level if the RSSI parameter is greater than or equal to the threshold.

The CCA level control signal may be included in the physical preamble of the transmission signal transmitted by the STA and transmitted.

It is understood by those skilled in the art that various changes and modifications can be made in the present invention without departing from the spirit or scope of the invention. Accordingly, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Reference is made herein to both apparatus and method inventions, and the descriptions of both apparatus and method inventions may be complementary to one another.

Various embodiments have been described in the best mode for carrying out the invention.

In the wireless communication system of the present invention, the data transmission and reception method has been described with reference to the example applied to the IEEE 802.11 system, but it is possible to apply to various wireless communication systems in addition to the IEEE 802.11 system.

Claims (13)

1. In the data transmission method of the STA (Station) device of a WLAN (Wireless LAN) system,

   Receiving a signal for another STA;

   Counting the number of ACK frames if the received signal comprises an ACK frame;

   Adjusting a CCA level based on the number of ACK frames counted during a particular time;

   When the received signal strength of the STA is greater than or equal to the adjusted CCA level, the wireless medium is detected in a busy condition. When the received signal strength is less than or equal to the adjusted CCA level, the wireless medium is idle. Detecting by; And

   Initiating data transmission when the wireless medium is in idle condition.
2. The method of claim 1,

   The adjusting of the CCA level may further include increasing the CCA level when the number of the ACK frames for the other STA is greater than or equal to a predetermined number.
3. The method of claim 1,

   Adjusting the CCA level, further comprising the step of reducing the CCA level when the number of the ACK frame for the other STA is less than a certain number.
4. The method of claim 1,

   The received signal includes a physical preamble, and the physical preamble further includes ACK frame identification information indicating whether the received signal corresponds to an ACK frame.
5. The method of claim 1,

   Acquiring received signal strength information using the received signal for the other STA;

   And adjusting the CCA level based on the received signal strength information in addition to the number of ACK frames.
6. The method of claim 5, wherein

   The received strength information is a Received Channel Power Indicator (RSSI) parameter, which maintains the CCA level when the RSSI parameter is greater than the threshold, and increases the CCA level when the RSSI parameter is greater than or equal to the threshold. Transmission method.
7. In the STA (Station) device of a wireless LAN (WLAN) system,

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

   A processor for controlling the RF unit; Including,

   The processor,

   Receiving a signal for another STA and counting the number of the ACK frame, if the received signal includes an ACK frame,

   Adjust a CCA level based on the number of ACK frames counted during a particular time period,

   When the received signal strength of the STA is greater than or equal to the adjusted CCA level, the wireless medium is detected in a busy condition. When the received signal strength is less than or equal to the adjusted CCA level, the wireless medium is idle. Detected by, and

   Initiating data transmission when the wireless medium is in idle condition.
8. The method of claim 7, wherein

   The adjustment of the CCA level is performed by increasing the CCA level when the number of the ACK frames for the other STA is a predetermined number or more.
9. The method of claim 7, wherein

   The adjustment of the CCA level is performed by reducing the CCA level when the number of the ACK frames for the other STA is less than a certain number.
10. The method of claim 7, wherein

    The received signal includes a physical preamble, and the physical preamble further includes ACK frame identification information indicating whether the received signal corresponds to an ACK frame.
11. The method of claim 7, wherein

    The processor acquires received signal strength information using the received signal for the other STA, and adjusts the CCA level based on the received signal strength information in addition to the number of the ACK frame.
12. The method of claim 11,

    The reception strength information is a Received Channel Power Indicator (RSSI) parameter.

    And the processor maintains the CCA level when the RSSI parameter is above the threshold and increases the CCA level when the RSSI parameter is above the threshold.
13. In the data transmission method of the STA device of the WLAN (Wireless LAN) system,

    Receiving a signal;

    Counting the number of ACK frames if the signal comprises an ACK frame; And

    Transmitting CCA level control information based on the number of ACK frames counted during a particular time;

    The CCA level control information is included in the physical preamble of the transmission signal of the STA and transmitted.

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