KR20110027539A - Method and apparatus of transmitting control signal in wlan system - Google Patents

Abstract

PURPOSE: A control signal transmission method of a wireless LAN system and an apparatus for supporting the same are provided to transmit a multiple data frame to a station and to secure the existence of a VHT station and a legacy station. CONSTITUTION: A frame generating unit generates a first control signal frame and a second control signal frame. A frame transmitting unit transmits the frame through multiple antennas. A VHT-SIG1(Very High Throughput-signal 1) field(230) includes common information about the SDMA transmission of the transmitted field. A VHT-SIG2 field(240) includes a parameter value which is used for transmitting SDMA(Spatial Division Multiple Access).

Description

Method for transmitting control signal in WLAN system and apparatus supporting same {Method and Apparatus of transmitting control signal in WLAN system}

The present invention relates to wireless communication, and more particularly, to a control signal transmission method and a device supporting the same in a wireless LAN system.

Recently, with the development of information and communication technology, various wireless communication technologies have been developed. Wireless LAN (WLAN) is based on radio frequency technology, using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc. It is a technology that allows wireless access to the Internet in a specific service area.

Since the Institute of Electrical and Electronics Engineers (IEEE) 802, the standardization body for WLAN technology, was established in February 1980, a number of standardization tasks have been performed.

Early WLAN technology used 2.4 GHz frequency through IEEE 802.11 to support speeds of 1 to 2 Mbps for frequency hopping, spread spectrum, infrared communication, etc. Can support speed. In addition, IEEE 802.11 improves Quality for Service (QoS), access point protocol compatibility, security enhancement, radio resource measurement, and wireless access vehicular environment. Standards of various technologies such as, fast roaming, mesh network, interworking with external network, and wireless network management are being put into practice.

Among IEEE 802.11, IEEE 802.11b supports communication speeds up to 11Mbs while using frequencies in the 2.4GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, reduces the influence of interference compared to the frequency of the congested 2.4 GHz band by using the frequency of the 5 GHz band instead of the 2.4 GHz band, and maximizes the communication speed by using OFDM technology. Up to 54Mbps. However, IEEE 802.11a has a shorter communication distance than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses a frequency of 2.4 GHz band to realize a communication speed of up to 54 Mbps and satisfies backward compatibility, thus receiving considerable attention. It is superior to

In order to overcome the limitation of communication speed, which has been pointed out as a weak point in WLAN, IEEE 802.11n is a relatively recent technical standard. 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) with data throughput of up to 540 Mbps and also uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. It is based on Multiple Inputs and Multiple Outputs (MIMO) technology. In addition, the standard not only uses a coding scheme for transmitting multiple duplicate copies to increase data reliability, but may also use orthogonal frequency division multiplex (OFDM) to increase the speed.

Background of the Invention As the spread of WLAN and applications diversifying using it have recently emerged, there is a need for a new WLAN system to support higher throughput than the data throughput supported by IEEE 802.11n. Very High Throughput (VHT) WLAN system is one of the recently proposed IEEE 802.11 WLAN system to support the data processing speed of 1Gbps or more. The name of the VHT WLAN system is arbitrary, and feasibility tests are currently being conducted on systems using 4X4 MIMO and 80 MHz or more channel bandwidth to provide throughput of 1 Gbps or more.

Currently, the VHT WLAN system under discussion has discussed two methods using a frequency band below 6 GHz and a 60 GHz band. In case of using a frequency band of 6 GHz or less, the possibility of coexistence with a conventional WLAN system using a frequency band of 6 GHz or less may be a problem.

Meanwhile, the IEEE 802.11 physical layer architecture (PHY layer architecture) is composed of a PHY Layer Management Entity (PLME), a Physical Layer Convergence Procedure (PLCP) sublayer, and a Physical Medium Dependent (PMD) sublayer. PLME cooperates with the MAC Layer Management Entity (MLME) to provide the management of the physical layer. The PLCP sublayer transfers the MAC Protocol Data Unit (MPDU) received from the MAC layer to the PMD sublayer according to the indication of the MAC layer between the MAC layer and the PMD layer, or delivers a frame from the PMD sublayer to the MAC layer. The PMD sublayer is a lower layer of the PLCP and enables transmission and reception of physical layer entities between two stations through a wireless medium.

The PLCP sublayer adds an additional field containing information required by the physical layer transceiver in the process of receiving the MPDU from the MAC layer and delivering it to the PMD sublayer. In this case, the added field may be a PLCP preamble, a PLCP header, and tail bits required on the data field. The PLCP preamble serves to prepare the receiver for synchronization and antenna diversity before the PSDU (PLCP Service Data Unit = MPDU) is transmitted. The PLCP header includes information about the frame, such as the length of the PSDU (PSDU Length Word. PLW), the data rate of the PSDU portion, and header error check information.

The PLCP sublayer adds the above-mentioned fields to the MPDU to generate a PPDU (PLCP Protocol Data Unit) and transmits it to the receiving station via the PMD sublayer, and the receiving station receives the PPDU to recover data from the PLCP preamble and PLCP header. Get the information and restore the data.

When various legacy stations such as IEEE 802.11 a / b / g / n and VHT stations coexist, legacy stations may not recognize or misbehave according to the PLCP format. To this end, when the PLCP format that can be recognized by the legacy station and the format for the VHT station are added to all transmission data so that all stations can recognize it, the overhead is large, which hinders the efficient use of radio resources. In addition, in a wireless LAN system supporting MU-MIMO, when a radio frame is transmitted by being spatially multiplexed (Spatial Division Multiple Access, SDMA) for multiple users, a station that is not a transmission target may not recognize this problem. In order to prevent the station from malfunctioning and smoothly transmit data, when the radio frame is transmitted to the station to be transmitted, the station not to be transmitted must also be recognized. There is a need to consider a new PLCP frame format to solve this problem.

One problem to be solved by the present invention is to provide a PLCP frame format used for SDMA data frames that are spatially multiplexed and transmitted for multiple users in a WLAN system supporting MU-MIMO.

One problem to be solved by the present invention is to provide a method for transmitting a PLCP frame used for the SDMA data frame that is spatially multiplexed for multiple users in a wireless LAN system supporting MU-MIMO.

The control signal transmission method according to the present invention includes transmitting the first control signal omni-directional and transmitting the second control signal, wherein the first control signal is a plurality of objects of the second control signal. Each station includes information necessary for receiving a second control signal, and the second control signal is beamformed and transmitted to the plurality of destination stations.

In a WLAN system supporting MU-MIMO, the coexistence of the VHT station and the legacy station can be ensured, and spatial multiplexed data frames for multiple users can be transmitted without interference from non-transmission stations.

1 is a diagram illustrating an example of a WLAN system to which an embodiment of the present invention may be applied.
2 is a block diagram illustrating an example of a PLCP frame format according to an embodiment of the present invention.
3 is an example of a VHT-Mixed-PLCP frame format and frame transmission according to an embodiment of the present invention.
4 is a block diagram illustrating a VHT-GF-PLCP frame format according to an embodiment of the present invention.
5 is a block diagram illustrating a wireless device in which an embodiment of the present invention is implemented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the embodiments described below, the MU-MIMO may be usefully applied to MU-MIMO transmission of multiplexed data for multiple users in a Very High Throughput (VHT) WLAN system operating in a frequency band of 6 GHz or less. It doesn't happen. The technical idea of the present invention described below may be equally applied to a wireless communication system that simultaneously transmits spatial multiplexed data to a plurality of stations regardless of a frequency band used.

1 is a diagram illustrating an example of a WLAN system to which an embodiment of the present invention may be applied. The WLAN system according to the example shown in FIG. 1 is a VHT (Very High Throughput) WLAN system.

Referring to FIG. 1, a WLAN system such as a VHT WLAN system includes one or more basic service sets (BSSs). The BSS is a set of stations (STAs) that can successfully synchronize and communicate with each other, and is not a concept indicating a specific area. As in a WLAN system to which an embodiment of the present invention can be applied, a BSS supporting ultra-high speed data processing of 1 GHz or more in a MAC SAP is referred to as a VHT (Very High Throughput) BSS.

The VHT BSS can also be classified into an infrastructure BSS and an independent BSS. The infrastructure BSS is illustrated in FIG. 1. Infrastructure BSS (BSS1, BSS2) is an access point (AP 1 (STA 2), AP that is a station that provides one or more non-AP STAs (STA 1, STA 3, STA 4), Distribution Service) 2 (STA 5)), and a Distribution System (DS) that connects multiple access points (AP 1, AP 2). In the infrastructure BSS, the AP STA manages the Non-AP STAs of the BSS.

Independent BSSs, on the other hand, are BSSs operating in ad-hoc mode. Since the IBSS does not include the AP VHT STA, there is no centralized management entity. That is, in the IBSS, Non-AP STAs are managed in a distributed manner. In the IBSS, all STAs may be configured as mobile stations, and access to the DS is not allowed to form a self-contained network.

A STA is any functional medium that includes a medium access control (MAC) compliant with the IEEE 802.11 standard and a physical layer interface to a wireless medium. Broadly speaking, an AP and a non-AP station (Non- AP Station). In addition, a STA that supports ultra-high speed data processing of 1 GHz or more in a multi-channel environment, which will be described later, is referred to as a VHT STA. In a VHT WLAN system to which an embodiment of the present invention can be applied, all of the STAs included in the BSS are VHT STAs, or both VHT STAs and legacy STAs (eg, HT STAs according to IEEE 802.11 a / b / g / n) coexist. You may.

The STA for wireless communication includes a processor and a transceiver, and includes a user interface and a display means. The processor is a functional unit designed to generate a frame to be transmitted through a wireless network or to process a frame received through the wireless network, and performs various functions for controlling an STA. The transceiver is a unit that is functionally connected to the processor and is designed to transmit and receive frames over a wireless network for a station.

Among the STAs, a portable terminal operated by a user is a non-AP STA (STA1, STA3, STA4, STA5), which may simply refer to a non-AP STA. A non-AP STA is a terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal, or a mobile subscriber. It may also be called another name such as a mobile subscriber unit. The non-AP STA supporting ultra-high speed data processing based on the MU-MIMO technology as described below is referred to as a non-AP VHT STA or simply a VHT STA.

The APs AP1 and AP2 are functional entities that provide access to the DS via a wireless medium for an associated station (STA) associated therewith. In an infrastructure BSS including an AP, communication between non-AP STAs is performed via an AP. However, when a direct link is established, direct communication between non-AP STAs is possible. The AP may be called a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller in addition to the access point. The AP supporting ultra-high speed data processing based on the MU-MIMO technology, which will be described later, is called a VHT AP.

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

The DS is a mechanism for one AP to communicate with another AP, which means that an AP transmits a frame for STAs coupled to a BSS managed by the AP or when one STA moves to another BSS. Frames can be delivered with external networks, such as wired networks. This DS does not necessarily need to be a network, and there is no limitation on its form as long as it can provide certain distribution services defined in IEEE 802.11. For example, the DS may be a wireless network such as a mesh network or a physical structure that connects APs with each other.

Meanwhile, the VHT WLAN system uses MU-MIMO in order for several STAs to efficiently use a wireless channel at the same time. In other words, multiple STAs simultaneously transmit and receive with the AP. The AP may transmit spatial multiplexed radio frames to several STAs. In addition, the channel condition may be measured to perform beamforming, and data may be transmitted and received through the beamformed channel path.

Hereinafter, a conventional STA except for a VHT STA is called a legacy STA. The legacy STA includes a non-HT STA supporting the IEEE 802.11 a / b / g standard and an HT STA supporting the IEEE 802.11n standard.

In a WLAN system, it is common to coexist with a VHT STA and a legacy STA. In addition, in case of MU-MIMO transmission, not all VHT STAs belonging to the BSS always transmit / receive with the AP. In this case, when a PLCP format that is not recognized by the legacy STA is used, the legacy STA may not recognize that data transmission is performed. Even when the BSS is made up of only VHT STAs, in a VHT WLAN system that transmits a spatial multiplexed frame to a plurality of stations by beamforming, a VHT STA that is not a transmission target cannot properly recognize a frame transmitted by an AP. This is because collision and interference problems between frames destined for different VHT STAs may occur, and transmission frames may not be received depending on the position of the STA due to the characteristics of beamforming transmission.

Therefore, when the VHT AP and the VHT STA transmits and receives a radio frame in the MU-MIMO method, it is necessary to let the VHT STA, which is not a radio frame transmission target, with the legacy STA to know that data is transmitted through the MU-MIMO. Do. Hereinafter, transmitting data by multiplexing the plurality of STAs is referred to as SDMA transmission.

To this end, the present invention proposes a PLCP frame format and a transmission method that can be recognized by a VHT STA or a legacy station that is not a transmission target in a WLAN system supporting MU-MIMO transmission.

2 is a block diagram illustrating an example of a PLCP frame format according to an embodiment of the present invention.

The VHT PLCP frame 200 includes a VHT-SIG1 field 230, a VHT-SIG2 field 240, and a data field 260. The VHT-SIG1 field 230 and the VHT-SIG2 field 240 include control information necessary for the receiving STA to demodulate and decode the data field 260, and the names thereof are arbitrary, and the first control information and the second control are respectively named. The information may be variously represented by the first control signal and the second control signal.

The VHT-SIG1 field 230 contains common information about the SDMA transmission of the field to be subsequently transmitted. The VHT-SIG1 field 230 may include information on a target STA of the VHT-SIG2 field 240 to be transmitted after all STAs in the BSS receive it and information necessary for receiving the VHT-SIG2 field 240. Common information may be further included in data transmission to the destination STA. For example, the SDMA transmission time may be indicated together with information about channel bandwidth information, modulation and coding information, and the number of spatial streams used. Information may be included. The SDMA transmission time is a time at which spatial division multiple access (SDMA) data, which is a spatial multiplexed data frame, is transmitted to a plurality of stations. STAs other than the transmission target may receive information indicating the SDMA transmission time, set a network allocation vector (NAV) and reserve channel access during the transmission period.

The VHT-SIG2 field 240 includes parameter values used for SDMA transmission for each transmission target STA. For example, the MCS index value indicating the Modulation and Coding Scheme (MCS) used, the bandwidth of the channel and the value indicating the number of spatial streams may be included. have.

The DATA field 260 may include SDMA precoded data to be transmitted to a transmission target STA and may further include tail bits and / or bit padding elements as necessary.

One or more VHT PLCP frames 200 contain frame timing acquisition, automatic gain control (AGC) convergence, diversity selection, information for channel estimation, and the like, as necessary. It may further include a field of. One or more of the fields described above may be a format that can be recognized by the legacy STA, or a field of a format that can be recognized by the legacy STA is further added.

The transmitting station transmitting the VHT PLCP frame 200 omni-directional transmissions of the VHT-SIG1 field 230 without SDMA precoding, the VHT-SIG2 field 240 and the data field 260 subsequently transmitted. And the like apply SDMA precoding and beamforming.

STAs of the BSS receive the VHT-SIG1 field 330 transmitted omnidirectionally without SDMA precoding, and an STA that does not correspond to a transmission target is transmitted during the period indicated by the SDMA transmission time information included in the VHT-SIG1 field 330. Channel access can be interrupted by setting NAV. The STA corresponding to the transmission target may receive information personalized to the user in the VHT-SIG2 field 340 to receive, demodulate, and decode the data transmitted to the STA.

3 is an example of a VHT-Mixed-PLCP frame format and frame transmission according to an embodiment of the present invention.

The VHT-Mixed-PLCP frame 300 includes a training field (TF) for a legacy STA (recognizable by the legacy STA) and a SIG, a TF and SIG for the VHT STA, and a data field. As an example of a training field (TF) and a SIG for a legacy STA, the VHT-Mixed-PLCP frame 300 of FIG. 2 includes a non-HT short training field 312 (L-STF) and a non-HT long training (L-LTF). field 314), L-SIG (Non-HT SIGNAL field 316), and HT-SIG (HT SIGNAL field 318).

The L-STF 312 is used for frame timing acquisition and automatic gain control (AGC) convergence, and the L-LTF 314 is used for the L-SIG 316 and data. It is used for channel estimation for demodulating the signal. The L-SIG 316 includes information for demodulating and decoding subsequent data. The HT-SIG 318 may be included in the L-SIG 316 and transmitted as a SIG field for the HT STA. The L-STF 312, L-LTF 314, and L-SIG 316 are transmitted in advance of other fields to allow the legacy STA to recognize them and know that the channel is in use.

VHT-Mixed-PLCP frame 300 according to an embodiment of the present invention is a VHT-STF 322, VHT-LTF1 324, two VHT-SIG (VHT-SIG1 330, VHT-) for the VHT STA SIG2 340) and VHT-LTFs 350-1, ..., 350-L. The VHT-SIG1 330 may include common information about a field to be transmitted later and a PLCP frame, and the VHT-SIG2 340 may include information personalized for each STA to which data is to be transmitted.

In the frame transmission method according to the embodiment of the present invention, the VHT-Mixed-PLCP frame 300 is transmitted first, and then N GF-PLCP frames 390-1,..., 390 -N are transmitted. The VHT-Mixed-PLCP frame 300 includes transmission time information of the VHT-Mixed-PLCP frame 300 and N GF-PLCP frames 390-1, ..., 390-N. The legacy STA and the VHT STAs other than the transmission destination STA recognize that the channel is used through the VHT-Mixed-PLCP frame 300 and use the channel based on the transmission time information included in the VHT-Mixed-PLCP frame 300. Set NAV for time and suspend channel access. To this end, the VHT-Mixed-PLCP frame 300 is transmitted without SDMA precoding so that all STAs including the legacy STA can be received until the VHT-SIG1 330, and is transmitted in the field transmitted after the VHT-SIG1 330. Only SDMA precoding is transmitted.

The legacy STA and the VHT STA other than the transmission purpose STA may not recognize the N GF-PLCP frames 390-1,..., 390 -N transmitted after the VHT-Mixed-PLCP frame 300, but are not VHT-Mixed. During the time required for transmission of both the VHT-Mixed-PLCP frame 300 and the N GF-PLCP frames 390-1,..., 390 -N based on the transmission period information included in the PLCCP frame 300. By setting the NAV to suspend channel access, malfunctions can be prevented.

4 is a block diagram illustrating a VHT-GF-PLCP frame format according to an embodiment of the present invention.

The VHT-GF-PLCP frame 400 includes VHT-GF-STF 410, VHT-LTF1 420, two VHT-SIG fields (VHT-SIG1 430, VHT-SIG2 440), N VHT LTF (450-1, ..., 450-N) and data fields. In the example of FIG. 4, the VHT-SIG1 430 and the VHT-SIG2 440 are continuously transmitted, but this is only an example, and the VHT-SIG2 440 is transmitted immediately after or after the VHT-SIG1 430 is transmitted. Can be. In the VHT-GF-PLCP frame 400 according to the present invention, the VHT-GF-STF 410, VHT-LTF1 420, and VHT-SIG1 430 fields are omni-directional so that all VHT STAs can listen. directional). The VHT-SIG2 440 field and subsequently transmitted data may be beamformed and transmitted through SDMA precoding. The VHT-SIG1 430 includes common information about SDMA transmissions to be subsequently transmitted. For example, the SDMA transmission period may be included so that third STAs other than the destination STA may configure the NAV during the transmission period. The VHT-SIG2 440 includes a parameter value used for SDMA transmission for each transmission target STA. For example, the MCS index, the channel bandwidth, the number of spatial streams, etc. may be set / included for each STA and transmitted.

Since the VHT-SIG2 440 field and subsequent data are beamformed and transmitted through SDMA precoding, a third STA other than the transmission destination STA does not receive the VHT-SIG2 440 field and subsequent data, but VHT The preamble may be recognized by receiving the SIG1 430 field.

In SU (Single User) -MIMO, the GF-PLCP frame may use one VHT SIG. This is because there is no collision or interference problem between PLCP frames destined for different STAs because SDMA transmission is not performed in SU-MIMO. In order to identify the GF-PLCP frame in SU-MIMO and MU-MIMO, the VHT SIG1 430 and the VHT SIG2 440 may include a type subfield indicating the transmission type. When the setting value of the type subfield indicates transmission of the SU-MIMO method, only one VHT SIG field is used. When the setting value of the type subfield indicates transmission of the MU-MIMO method, two VHT SIGs (VHT SIG1 and VHT SIG2) are used. As described above, the two VHT SIGs are transmitted omnidirectionally so that the STAs in the BSS can detect / recognize the preambles of the PLCP frames being transmitted, and the VHT SIG2 is the MCS for the spatial streams destined for each transmission destination STA. It contains information such as an index value, channel bandwidth, and number of spatial streams.

5 is a block diagram illustrating a wireless device in which an embodiment of the present invention is implemented. The wireless device may be part of an AP or a non-AP STA.

The wireless device 500 includes a frame generator 515 and a frame transmitter 535. The frame generator generates a PLCP frame according to the above-described embodiment. The frame transmitter transmits the generated frame through multiple antennas.

The frame generator and the frame transmitter may be implemented as one chip in the form of a processor. An embodiment of generating a frame may be configured as a software module, stored in memory, and executed by a processor.

6 is a block diagram illustrating another example of a wireless device in which an embodiment of the present invention is implemented. Wireless device 600 may be an AP or a non-AP station.

The wireless device 600 includes a processor 510, a memory 620, a transceiver 630, and N antennas 650-1 ... 650 -N. The transceiver 630 transmits / receives a radio signal but implements a physical layer of IEEE 802.11. The transceiver 630 supports MIMO transmission through N antennas 650-1. The processor 610 is connected to the transceiver 630 to implement the MAC layer and the physical layer of IEEE 802.11. When the processor 610 processes the operation of the transmission station in the foregoing method, the wireless device 600 becomes the transmission station. When the processor 610 handles the operation of the receiving station of the foregoing method, the wireless device 600 becomes the receiving station.

The PLCP sublayer of the transmission station implemented in the processor 610 attaches a PLCP preamble and a PLCP header to the PSDU transmitted from the MAC layer based on the PLCP frame format described above and sends it to the PMD sublayer implemented in the processor 610. The PMD sublayer transmits the PLCP frame through the transceiver 630 based on the field-specific transmission method of the PLCP frame format using the multiple antenna system. The PLCP sublayer of the receiving station implemented in the processor 610 of the receiving station removes the PLCP preamble and the PLCP header based on the PLCP frame format described above, and sends the PSDU to the MAC layer implemented in the processor 610 of the receiving station.

The processor 610 and / or the transceiver 630 may include an application-specific integrated circuit (ASIC), another chipset, logic circuit, and / or data processing device. The memory 620 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and / or other storage device. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above. The module may be stored in the memory 620 and executed by the processor 610. The memory 620 may be inside or outside the processor 610 and may be connected to the processor 610 by various well-known means.

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

Claims (8)

In the control signal transmission method in a wireless LAN system,
Transmit the first control signal omni-directional,
Including transmitting a second control signal,
The first control signal includes information necessary for each of the plurality of destination stations of the second control signal to receive the second control signal,
And the second control signal is beamformed and transmitted to the plurality of destination stations. The method of claim 1,
And the first control signal further includes transmission time information for transmitting spatial division multiple access (SDMA) data to the plurality of destination stations. The method of claim 1,
And wherein the second control signal includes control information for each of the plurality of destination stations. The method of claim 3, wherein
The control information for each of the plurality of destination stations is at least one of modulation and coding scheme (MCS) information, channel bandwidth information, spatial stream number information, and transmission power information. The method of claim 1,
The first control signal and the second control signal is transmitted through a first frame,
The second control signal may further include transmission time information required for transmitting one or more second frames transmitted after the first frame. The method of claim 1,
And transmitting a first LTF (Long Training Field) for channel estimation used for receiving the first control signal before transmitting the first control signal. The method of claim 1,
And transmitting a data field after transmitting the second control signal, wherein the second control signal transmission and the data field are beamformed using the same precoding matrix. In a wireless device for transmitting a control signal in a wireless LAN system,
A frame generation unit generating a frame including a first control signal containing information necessary to receive a second control signal and the second control signal containing control information for a plurality of destination stations; And
And a frame transmitter for transmitting the frame through multiple antennas.

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