WO2017069349A1 - Method for transmitting data in wireless communication system, and device therefor - Google Patents

Abstract

According to one embodiment of the present invention, an uplink (UL) multi-user (MU) transmission method of a station (STA) device in a wireless LAN (WLAN) system comprises the steps of: transmitting a resource request to an access point (AP); receiving a buffer state request from the AP; transmitting buffer state information to the AP; receiving, from the AP, trigger information for UL MU transmission; and transmitting, by using an orthogonal frequency division multiple access (OFDMA) scheme, a UL MU frame including at least one resource unit, on the basis of the trigger information.

Description

Method for transmitting data in wireless communication system and apparatus therefor

The present invention relates to a wireless communication system, and more particularly, to a data transmission method for supporting multi-user ACK frame transmission and an apparatus supporting the same.

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 60 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 160 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 task group, also known as IEEE 802.11ax or High Efficiency (HEW) WLAN, includes: 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.

An object of the present invention is to propose an uplink multi-user transmission method in a wireless communication system. In particular, the present invention proposes a resource request method and a buffer state information transmission method for uplink multi-user transmission.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

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

In a WLAN wireless LAN (WLAN) system according to an embodiment of the present invention, an uplink (UL) multi-user (MU) transmission method of a station (STA) device may request a resource to an access point (AP). Transmitting; Receiving a buffer status request from the AP; Transmitting buffer status information to the AP; Receiving trigger information for UL MU transmission from the AP; And transmitting an UL MU frame including at least one resource unit based on the trigger information using an orthogonal frequency division multiple access (OFDMA) scheme.

In the UL MU transmission method according to an embodiment of the present invention, the trigger information may include resource unit allocation information for the UL MU frame transmission and length information of a UL MU frame.

In addition, in the UL MU transmission method according to an embodiment of the present invention, the buffer status information may indicate the amount of queued traffic of the STA device.

In addition, in the UL MU transmission method according to an embodiment of the present invention, the resource request may be a signal frame including a High Efficiency (HE) -Long Training Field (LTF) sequence occupying a specific resource unit.

In addition, the UL MU transmission method according to an embodiment of the present invention may further include receiving resource unit allocation information indicating allocation of the resource unit to transmit the resource request.

In addition, in the UL MU transmission method according to an embodiment of the present invention, the buffer status request may be received through the specific resource unit to which the resource request is transmitted.

In a wireless LAN (WLAN) system according to an embodiment of the present invention, an STA (Station) device transmits and receives a radio signal; And a processor for controlling the RF unit, wherein the STA device transmits a resource request to an access point, receives a buffer status request from the AP, and transmits buffer status information to the AP. Trigger information for UL MU transmission is received from the AP, and a UL MU frame including at least one resource unit may be transmitted using an orthogonal frequency division multiple access (OFDMA) scheme based on the trigger information.

In the STA apparatus according to the embodiment of the present invention, the trigger information may include resource unit allocation information for the UL MU frame transmission and length information of a UL MU frame.

In addition, in the STA apparatus according to the embodiment of the present invention, the buffer status information may indicate the amount of queued traffic of the STA apparatus.

In addition, in the STA apparatus according to an embodiment of the present invention, the resource request may be a signal frame including a High Efficiency (HE) -Long Training Field (LTF) sequence occupying a specific resource unit.

In addition, the STA apparatus according to an embodiment of the present invention may receive resource unit allocation information indicating allocation of the resource unit to which the resource request is to be transmitted.

Further, in the STA apparatus according to the embodiment of the present invention, the buffer status request may be received through the specific resource unit in which the resource request is transmitted.

According to the present invention, by using a resource unit request method for UL MU transmission and buffer status information according to the same, a UL MU transmission procedure can be further simplified by omitting transmission and reception of ACK information.

In addition, the STA of the present invention may perform a resource request by transmitting a HE-LTF sequence using a specific resource unit or a combination of a specific resource unit and STBC. Thus, the AP can quickly respond to the resource request. The STA may also send the resource request more simply. Resource requests can also be sent to the UL MU, thereby improving space usage efficiency.

The present invention can quickly and efficiently proceed with the resource request and allocation process by transmitting resource allocation information through the resource received on the resource request date. In addition, the present invention can further simplify the communication procedure for UL MU transmission by exchanging buffer status request and buffer status information immediately after resource allocation.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, included as part of the detailed description in order to provide a thorough understanding of the present invention, provide embodiments of the present invention and together with the description, describe the technical features of the present invention.

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

FIG. 6 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.

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

8 is a diagram conceptually illustrating a channel sounding method in a wireless communication system to which the present invention can be applied.

9 is a diagram illustrating a VHT NDPA frame in a wireless communication system to which the present invention can be applied.

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

FIG. 11 is a diagram illustrating a VHT compressed beamforming frame format in a wireless communication system to which the present invention can be applied.

FIG. 12 is a diagram illustrating a beamforming report poll frame format in a wireless communication system to which the present invention can be applied.

FIG. 13 is a diagram illustrating a downlink multi-user PPDU format in a wireless communication system to which the present invention can be applied.

14 is a diagram illustrating a downlink multi-user PPDU format in a wireless communication system to which the present invention can be applied.

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

16 is a diagram illustrating an ACK frame in a wireless communication system to which the present invention can be applied.

17 is a diagram illustrating a block ACK request frame in a wireless communication system to which the present invention can be applied.

FIG. 18 illustrates a BAR information field of a block ACK request frame in a wireless communication system to which an embodiment of the present invention may be applied.

19 is a diagram illustrating a block ACK (block Ack) frame in a wireless communication system to which the present invention can be applied.

FIG. 20 is a diagram illustrating a BA Information field of a block ACK frame in a wireless communication system to which an embodiment of the present invention may be applied.

21 through 23 are diagrams illustrating an HE format PPDU according to an embodiment of the present invention.

24 is a diagram illustrating an uplink multi-user transmission procedure according to an embodiment of the present invention.

25 to 27 illustrate a resource allocation unit in an OFDMA multi-user transmission scheme according to an embodiment of the present invention.

28 illustrates a resource request method according to an embodiment of the present invention.

29 illustrates a method of resource allocation and UL MU reception according to an embodiment of the present invention.

30 illustrates a resource allocation and a UL MU reception method according to an embodiment of the present invention.

31 is a flowchart illustrating a UL MU transmission method of an STA apparatus according to an embodiment of the present invention.

32 is a block diagram of each STA apparatus according to an embodiment of the present invention.

The terminology used herein is a general term that has been widely used as far as possible in consideration of the functions in the present specification, but may vary according to the intention of a person skilled in the art, convention or the emergence of a new technology. In addition, in certain cases, there is a term arbitrarily selected by the applicant, and in this case, the meaning will be described in the description of the corresponding embodiment. Therefore, it is to be understood that the terminology used herein is to be interpreted based not on the name of the term but on the actual meaning and contents throughout the present specification.

Moreover, although the embodiments will be described in detail with reference to the accompanying drawings and the contents described in the accompanying drawings, the present invention is not limited or restricted to the embodiments.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

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 may be implemented with wireless technologies such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (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.

Table 1 below is a table illustrating the HT-SIG field.

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 16 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.

Table 2 is a table illustrating the VHT-SIG-A1 field.

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.

Table 3 is a table illustrating the VHT-SIG-A2 field.

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 decodes the VHT-SIG-B field only when common control information included in the VHT-SIG-A field indicates that the currently received PPDU indicates MU-MIMO transmission. It can be designed to. 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 160 MHz transmission and 80 + 80 MHz, first the VHT-SIG-B bits are repeated four times, as with the 80 MHz transmission, with pad bits set to zero 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.

MAC frame format

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

Referring to FIG. 5, 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. Bits 5-6 of the QoS Control field may be configured as an ACK policy field, and Table 4 is a table illustrating an ACK policy field in the QoS control field.

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. 6 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. 6, 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.

7 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. 7, 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 voluntary MFB (Unsolicited MFB) subfield.

Table 5 shows a description of each subfield included in the HT Control Middle subfield of the VHT format.

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.

Channel State Information Feedback Method

SU-MIMO technology, in which a beamformer assigns all antennas to one beamformee and communicates, increases channel capacity through diversity gain and stream multiplexing using space-time. . SU-MIMO technology can contribute to improving the performance of the physical layer by increasing the number of antennas by increasing the number of antennas compared to when the MIMO technology is not applied.

In addition, the MU-MIMO technology, in which a beamformer allocates antennas to a plurality of beamformees, provides a link layer protocol for multiple access of a plurality of beamformees connected to the beamformer. It can improve performance.

In the MIMO environment, how accurately the beamformer knows the channel information can have a big impact on the performance, so a feedback procedure for channel information acquisition is required.

There are two types of feedback procedures for obtaining channel information. One is to use a control frame, and the other is to use a channel sounding procedure that does not include a data field. Sounding means using the corresponding training field to measure the channel for purposes other than data demodulation of the PPDU including the preamble training field.

Hereinafter, the channel information feedback method using a control frame and the channel information feedback method using a null data packet (NDP) will be described in more detail.

1) Feedback method using control frame

In the MIMO environment, Beamformer may instruct feedback of channel state information through the HT control field included in the MAC header, or Beamformee may report channel state information through the HT control field included in the MAC frame header (see FIG. 8). . The HT control field may be included in a control frame or a QoS data frame in which the Order subfield of the MAC header is set to 1, and the management frame.

2) Feedback method using channel sounding

8 is a diagram conceptually illustrating a channel sounding method in a wireless communication system to which the present invention can be applied.

FIG. 8 illustrates a method of feeding back channel state information between a Beamformer (eg, AP) and a Beamformee (eg, a non-AP STA) based on a sounding protocol. The sounding protocol may refer to a procedure for receiving feedback on channel state information.

The channel state information sounding method between the beamformer and the beamformee based on the sounding protocol may be performed by the following steps.

(1) The beamformer transmits a VHT NDPA (VHT Null Data Packet Announcement) frame indicating a sounding transmission for feedback of the beamformee.

The VHT NDPA frame refers to a control frame used to indicate that channel sounding is started and that NDP (Null Data Packet) will be transmitted. In other words, by transmitting the VHT NDPA frame before transmitting the NDP, Beamformee may prepare to feed back channel state information before receiving the NDP frame.

The VHT NDPA frame may include AID (association identifier) information, feedback type information, etc. of the Beamformee to transmit the NDP. A more detailed description of the VHT NDPA frame will be given later.

The VHT NDPA frame may be transmitted in a different transmission method when data is transmitted using MU-MIMO and when data is transmitted using SU-MIMO. For example, when performing channel sounding for MU-MIMO, a VHT NDPA frame is transmitted in a broadcast manner, but when channel sounding for SU-MIMO is performed, a VHT NDPA frame is transmitted to one target STA. Can be transmitted in a unicast manner.

(2) Beamformer transmits NDP after SIFS time after transmitting VHT NDPA frame. NDP has a VHT PPDU structure excluding data fields.

Beamformees receiving the VHT NDPA frame may check the value of the AID12 subfield included in the STA information field, and may determine whether the beamformee is a sounding target STA.

In addition, the beamformees may know the feedback order through the order of the STA Info field included in the NDPA. 11 illustrates a case in which the feedback order is performed in the order of Beamformee 1, Beamformee 2, and Beamformee 3.

(3) Beamformee 1 obtains downlink channel state information based on a training field included in the NDP, and generates feedback information to be transmitted to the beamformer.

Beamformee 1 transmits a VHT compressed beamforming frame including feedback information to the beamformer after SIFS after receiving the NDP frame.

The VHT Compressed Beamforming frame may include an SNR value for a space-time stream, information about a compressed beamforming feedback matrix for a subcarrier, and the like. A more detailed description of the VHT Compressed Beamforming frame will be described later.

(4) After receiving the VHT Compressed Beamforming frame from Beamformee 1, the beamformer transmits a Beamforming Report Poll frame to Beamformee 2 to obtain channel information from Beamformee 2 after SIFS.

The Beamforming Report Poll frame is a frame that performs the same role as the NDP frame, and Beamformee 2 may measure a channel state based on the transmitted Beamforming Report Poll frame.

A more detailed description of the beamforming report poll frame frame will be described later.

(5) Beamforming Report After receiving the Poll frame, Beamformee 2 transmits the VHT Compressed Beamforming frame including feedback information to the beamformer after SIFS.

(6) After receiving the VHT Compressed Beamforming frame from Beamformee 2, the beamformer transmits a Beamforming Report Poll frame to Beamformee 3 to obtain channel information from Beamformee 3 after SIFS.

(7) Beamforming Report After receiving the Poll frame, Beamformee 3 transmits the VHT Compressed Beamforming frame including feedback information to the beamformer after SIFS.

Hereinafter, a frame used in the aforementioned channel sounding procedure will be described.

9 is a diagram illustrating a VHT NDPA frame in a wireless communication system to which the present invention can be applied.

9, a VHT NDPA frame includes a frame control field, a duration field, a receiving address field, a transmitting address field, a sounding dialog token field, It may be composed of a STA Info 1 field, a STA Info n field, and an FCS.

The RA field value indicates a receiver address or STA address for receiving a VHT NDPA frame.

If the VHT NDPA frame includes one STA Info field, the RA field value has the address of the STA identified by the AID in the STA Info field. For example, when transmitting a VHT NDPA frame to one target STA for SU-MIMO channel sounding, the AP transmits the VHT NDPA frame to the target STA by unicast.

On the other hand, when the VHT NDPA frame includes one or more STA Info fields, the RA field value has a broadcast address. For example, when transmitting a VHT NDPA frame to at least one target STA for MU-MIMO channel sounding, the AP broadcasts a VHT NDPA frame.

The TA field value represents a transmitter address for transmitting a VHT NDPA frame or an address of a transmitting STA or a bandwidth for signaling a TA.

The Sounding Dialog Token field may be referred to as a sounding sequence field. The Sounding Dialog Token Number subfield in the Sounding Dialog Token field contains a value selected by the Beamformer to identify the VHT NDPA frame.

The VHT NDPA frame includes at least one STA Info field. That is, the VHT NDPA frame includes a STA Info field that includes information about the sounding target STA. One STA Info field may be included for each sounding target STA.

Each STA Info field may be composed of an AID12 subfield, a feedback type subfield, and an Nc index subfield.

Table 6 shows subfields of the STA Info field included in the VHT NDPA frame.

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 a MAC frame, and may be replaced with another field or further fields may be included.

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

Referring to FIG. 10, the NDP may have a format in which a data field is omitted from the VHT PPDU format shown in FIG. 4. The NDP may be precoded based on a specific precoding matrix and transmitted to the sounding target STA.

In the L-SIG field of the NDP, the length field indicating the length of the PSDU included in the data field is set to '0'.

In the VHT-SIG-A field of the NDP, the Group ID field indicating whether the transmission scheme used for NDP transmission is MU-MIMO or SU-MIMO is set to a value indicating SU-MIMO transmission.

The data bits of the VHT-SIG-B field of the NDP are set to a fixed bit pattern for each bandwidth.

When the sounding target STA receives the NDP, the sounding target STA estimates a channel based on the VHT-LTF field of the NDP and obtains channel state information.

FIG. 11 is a diagram illustrating a VHT compressed beamforming frame format in a wireless communication system to which the present invention can be applied.

Referring to FIG. 11, the VHT compressed beamforming frame is a VHT action frame for supporting the VHT function and includes an action field in the frame body. The Action field is included in the Frame Body of the MAC frame to provide a mechanism for specifying extended management operations.

The Action field includes the Category field, the VHT Action field, the VHT MIMO Control field, the VHT Compressed Beamforming Report field, and the MU Exclusive Beamforming. Report) field.

The Category field is set to a value indicating a VHT category (ie, a VHT Action frame), and the VHT Action field is set to a value indicating a VHT Compressed Beamforming frame.

The VHT MIMO Control field is used to feed back control information related to beamforming feedback. The VHT MIMO Control field may always be present in the VHT Compressed Beamforming frame.

The VHT Compressed Beamforming Report field is used to feed back information about a beamforming metric including SNR information about a space-time stream used to transmit data.

The MU Exclusive Beamforming Report field is used to feed back SNR information on a spatial stream when performing MU-MIMO transmission.

The presence and content of the VHT Compressed Beamforming Report field and the MU Exclusive Beamforming Report field are determined by the Feedback Type subfield, the Remaining Feedback Segments subfield, and the First Feedback Segment of the VHT MIMO Control field. Feedback Segment) may be determined according to the value of the subfield.

Hereinafter, the VHT MIMO Control field, the VHT Compressed Beamforming Report field, and the MU Exclusive Beamforming Report field will be described in more detail.

1) The VHT MIMO Control field includes an Nc Index subfield, an Nr Index subfield, a Channel Width subfield, a Grouping subfield, a Codebook Information subfield, Feedback Type Subfield, Remaining Feedback Segments Subfield, First Feedback Segment Subfield, Reserved Subfield, and Sounding Dialog Token Number Sub It consists of fields.

Table 7 shows subfields of the VHT MIMO Control field.

If the VHT Compressed Beamforming frame does not carry all or part of the VHT Compressed Beamforming Report field, the Nc Index subfield, Channel Width subfield, Grouping subfield, Codebook Information subfield, Feedback Type subfield, and Sounding Dialog Token Number subfield Is set to a preliminary field, the First Feedback Segment subfield is set to '0', and the Remaining Feedback Segments subfield is set to '7'.

The Sounding Dialog Token Number subfield may be called a Sounding Sequence Number subfield.

2) The VHT compressed beamforming report field contains explicit feedback in the form of angles of the compressed beamforming feedback matrix 'V' which the transmitting beamformer uses to determine the steering matrix 'Q'. It is used to convey information.

Table 8 shows subfields of the VHT compressed beamforming report field.

Referring to Table 8, the VHT compressed beamforming report field may include an average SNR for each space-time stream and a compressed beamforming feedback matrix 'V' for each subcarrier. The compressed beamforming feedback matrix is used to calculate a channel matrix (ie, steering matrix 'Q') in a transmission method using MIMO as a matrix including information on channel conditions.

scidx () means a subcarrier through which the Compressed Beamforming Feedback Matrix subfield is transmitted. Na is fixed by the value of Nr × Nc (for example, φ11, Ψ21, ... when Nr × Nc = 2 × 1).

Ns denotes the number of subcarriers through which the compressed beamforming feedback matrix is transmitted to the beamformer. Beamformee can reduce the number of Ns through which the compressed beamforming feedback matrix is transmitted using a grouping method. For example, the number of compressed beamforming feedback matrices fed back may be reduced by grouping a plurality of subcarriers into one group and transmitting the compressed beamforming feedback matrix for each group. Ns may be calculated from the Channel Width subfield and the Grouping subfield included in the VHT MIMO Control field.

Table 9 illustrates an average SNR of Space-Time (SNR) Stream subfield of a space-time stream.

Referring to Table 9, the average SNR for each space-time stream is calculated by calculating an average SNR value for all subcarriers included in the channel and mapping the value to a range of -128 to +128.

3) The MU Exclusive Beamforming Report field is used to convey explicit feedback information in the form of delta SNR. Information in the VHT Compressed Beamforming Report field and the MU Exclusive Beamforming Report field may be used by the MU Beamformer to determine the steering matrix 'Q'.

Table 10 shows subfields of an MU Exclusive Beamforming Report field included in a VHT compressed beamforming frame.

Referring to Table 10, the MU Exclusive Beamforming Report field may include SNR per space-time stream for each subcarrier.

Each Delta SNR subfield has an increment of 1 dB between -8 dB and 7 dB.

scidx () denotes subcarrier (s) in which the Delta SNR subfield is transmitted, and Ns denotes the number of subcarriers in which the Delta SNR subfield is transmitted to the beamformer.

FIG. 12 is a diagram illustrating a beamforming report poll frame format in a wireless communication system to which the present invention can be applied.

Referring to FIG. 12, the Beamforming Report Poll frame includes a Frame Control field, a Duration field, a Receiving Address (RA) field, a TA (Transmitting Address) field, and a Feedback Segment Retransmission Bitmap. ) Field and the FCS.

The RA field value indicates the address of the intended recipient.

The TA field value indicates an address of an STA transmitting a Beamforming Report Poll frame or a bandwidth signaling a TA.

The Feedback Segment Retransmission Bitmap field indicates a feedback segment requested in a VHT Compressed Beamforming report.

If the bit in position n in the Feedback Segment Retransmission Bitmap field value is '1' (n = 0 for LSB, n = 7 for MSB), then the n corresponds to n in the Remaining Feedback Segments subfield in the VHT MIMO Control field of the VHT compressed beamforming frame. Feedback segments are requested. On the other hand, if the bit of position n is '0', the feedback segment corresponding to n is not requested in the Remaining Feedback Segments subfield in the VHT MIMO Control field.

Downlink MU- MIMO  Frame (DL MU- MIMO  Frame)

FIG. 13 is a diagram illustrating a downlink multi-user PPDU format in a wireless communication system to which the present invention can be applied.

Referring to FIG. 13, a PPDU includes a physical preamble and a data field. The data field may include a service field, a scrambled PSDU field, tail bits, and padding bits.

The AP may aggregate the MPDUs and transmit a data frame in an A-MPDU (aggregated MPDU) format. In this case, the scrambled PSDU field may be configured as an A-MPDU.

An A-MPDU consists of a sequence of one or more A-MPDU subframes.

For the VHT PPDU, since the length of each A-MPDU subframe is a multiple of four octets, the A-MPDU is zero after the last A-MPDU subframe to fit the A-MPDU to the last octet of the PSDU. And three to three octets of an end-of-frame (EOF) pad.

The A-MPDU subframe consists of an MPDU delimiter, and optionally an MPDU may be included after the MPDU delimiter. In addition, except for the last A-MPDU subframe in one A-MPDU, a pad octet is attached after the MPDU to make the length of each A-MPDU subframe a multiple of 4 octets.

The MPDU Delimiter is composed of a Reserved field, an MPDU Length field, a cyclic redundancy check (CRC) field, and a delimiter signature field.

In the case of a VHT PPDU, the MPDU Delimiter may further include an end-of-frame (EOF) field. If the MPDU Length field is 0 and the A-MPDU subframe used for padding or the A-MPDU subframe carrying the MPDU when the A-MPDU consists of only one MPDU, the EOF field is set to '1'. do. Otherwise it is set to '0'.

The MPDU Length field contains information about the length of the MPDU.

If the MPDU does not exist in the corresponding A-MPDU subframe, it is set to '0'. An A-MPDU subframe whose MPDU Length field has a value of '0' is used when padding the corresponding A-MPDU to match the A-MPDU to the octets available in the VHT PPDU.

The CRC field includes CRC information for error checking, and the Delimiter Signature field includes pattern information used to search for an MPDU delimiter.

The MPDU is composed of a MAC header, a frame body, and a frame check sequence (FCS).

14 is a diagram illustrating a downlink multi-user PPDU format in a wireless communication system to which the present invention can be applied.

14 assumes that the number of STAs receiving the PPDU is three and the number of spatial streams allocated to each STA is 1, but the number of STAs paired to the AP and the number of spatial streams allocated to each STA are shown in FIG. Is not limited to this.

Referring to FIG. 14, the MU PPDU includes L-TFs field (L-STF field and L-LTF field), L-SIG field, VHT-SIG-A field, VHT-TFs field (VHT-STF field and VHT-LTF). Field), VHT-SIG-B field, Service field, one or more PSDU, padding field, and Tail bit. Since the L-TFs field, the L-SIG field, the VHT-SIG-A field, the VHT-TFs field, and the VHT-SIG-B field are the same as in the example of FIG. 4, detailed descriptions thereof will be omitted.

Information for indicating the duration of the PPDU may be included in the L-SIG field. Within the PPDU, the PPDU duration indicated by the L-SIG field is the symbol assigned to the VHT-SIG-A field, the symbol assigned to the VHT-TFs field, the field assigned to the VHT-SIG-B field, and the Service field. And bits constituting the bits, bits constituting the PSDU, bits constituting the padding field, and bits constituting the Tail field. The STA receiving the PPDU may obtain information about the duration of the PPDU through the information indicating the duration of the PPDU included in the L-SIG field.

As described above, Group ID information and space-time stream number information per user are transmitted through the VHT-SIG-A, and a coding method and MCS information are transmitted through the VHT-SIG-B. Accordingly, the beamformees may check the VHT-SIG-A and the VHT-SIG-B, and may know whether the beamformees belong to the MU MIMO frame. Therefore, the STA that is not a member STA of the corresponding Group ID or the member of the corresponding Group ID or the number of allocated streams is '0' reduces power consumption by setting to stop receiving the physical layer from the VHT-SIG-A field to the end of the PPDU. can do.

The Group ID can receive the Group ID Management frame transmitted by the Beamformer in advance, so that the MU group belonging to the Beamformee and the user of the group to which the Beamformee belongs, that is, the stream through which the PPDU is received.

All MPDUs transmitted in the VHT MU PPDU based on 802.11ac are included in the A-MPDU. In the data field of FIG. 18, each VHT A-MPDU may be transmitted in a different stream.

In FIG. 14, since the size of data transmitted to each STA may be different, each A-MPDU may have a different bit size.

In this case, null padding may be performed such that the time when the transmission of the plurality of data frames transmitted by the beamformer is the same as the time when the transmission of the maximum interval transmission data frame is terminated. The maximum interval transmission data frame may be a frame in which valid downlink data is transmitted by the beamformer for the longest period. The valid downlink data may be downlink data that is not null padded. For example, valid downlink data may be included in the A-MPDU and transmitted. Null padding may be performed on the remaining data frames except the maximum interval transmission data frame among the plurality of data frames.

For null padding, the beamformer may encode and fill one or more A-MPDU subframes located in temporal order in the plurality of A-MPDU subframes in the A-MPDU frame with only the MPDU delimiter field. An A-MPDU subframe having an MPDU length of 0 may be referred to as a null subframe.

As described above, in the null subframe, the EOF field of the MPDU Delimiter is set to '1'. Accordingly, when the MAC layer of the receiving STA detects the EOF field set to 1, power consumption may be reduced by setting the physical layer to stop reception.

block ACK (Block Ack ) step

15 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, physical 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.

ACK (Acknowledgement) / block ACK (Block ACK ) frame

In general, an ACK frame is used as a response to the MPDU, and a block ACK frame is used as a response to the A-MPDU.

16 is a diagram illustrating an ACK frame in a wireless communication system to which the present invention can be applied.

Referring to FIG. 16, an ACK frame is composed of a frame control field, a duration field, an RA field, and an FCS.

The RA field may be a second address field of a data frame, a management frame, a block ACK request frame, a block ACK frame, or a PS-Poll frame received immediately before. It is set to the value of.

When the ACK frame is transmitted by the non-QoS STA, the More Fragments subfield in the Frame Control field of the data frame or management frame received immediately before If '0', the duration value is set to '0'.

In an ACK frame that is not transmitted by a non-QoS STA, the duration value may include a data frame, a management frame, a block ACK request frame, a block received immediately before. In the Duration / ID field of the ACK (Block Ack) frame or the PS-Poll frame, the time required for transmitting the ACK frame and the SIFS interval are set to a value (ms). If the calculated duration value is not an integer value, it is rounded up.

Hereinafter, a block ACK (request) frame will be described.

17 is a diagram illustrating a block ACK request frame in a wireless communication system to which the present invention can be applied.

Referring to FIG. 17, a block ACK request (BAR) frame includes a frame control field, a duration / ID field, a reception address field, a transmission address field, a BAR control ( BAR control field, BAR information field and frame check sequence (FCS).

The RA field may be set to the address of the STA that receives the BAR frame.

The TA field may be set to an address of an STA that transmits a BAR frame.

The BAR control field includes a BAR Ack Policy subfield, a Multi-TID subfield, a Compressed Bitmap subfield, a Reserved subfield, and a TID Information (TID_Info) subfield. It includes.

Table 11 is a table illustrating a BAR control field.

The BAR Information field contains different information according to the type of the BAR frame. This will be described with reference to FIG. 18.

FIG. 18 illustrates a BAR information field of a block ACK request frame in a wireless communication system to which an embodiment of the present invention may be applied.

FIG. 18A illustrates a BAR Information field of a Basic BAR frame and a Compressed BAR frame, and FIG. 22B illustrates a BAR Information field of a Multi-TID BAR frame.

Referring to FIG. 18A, in the case of a Basic BAR frame and a Compressed BAR frame, the BAR Information field includes a Block Ack Starting Sequence Control subfield.

The Block Ack Starting Sequence Control subfield includes a fragment number subfield and a starting sequence number subfield.

The Fragment Number subfield is set to zero.

In the case of a Basic BAR frame, the Starting Sequence Number subfield includes the sequence number of the first MSDU in which the corresponding BAR frame is transmitted. In the case of a compressed BAR frame, the Starting Sequence Control subfield includes the sequence number of the first MSDU or A-MSDU for which the corresponding BAR frame is to be transmitted.

Referring to FIG. 18B, in the case of a multi-TID BAR frame, the BAR Information field may include a TID Info subfield and a Block Ack Starting Sequence Control subfield in one or more TIDs. Stars are repeated.

The Per TID Info subfield includes a reserved subfield and a TID value subfield. The TID Value subfield contains a TID value.

The Block Ack Starting Sequence Control subfield includes the Fragment Number and Starting Sequence Number subfields as described above. The Fragment Number subfield is set to zero. The Starting Sequence Control subfield includes the sequence number of the first MSDU or A-MSDU for which the corresponding BAR frame is to be transmitted.

19 is a diagram illustrating a block ACK (block Ack) frame in a wireless communication system to which the present invention can be applied.

Referring to FIG. 19, a block ACK (BA) frame includes a frame control field, a duration / ID field, a reception address field, a transmission address field, and a BA control BA. control field, BA Information field, and frame check sequence (FCS).

The RA field may be set to the address of the STA requesting the block ACK.

The TA field may be set to an address of an STA that transmits a BA frame.

The BA control field includes a BA Ack Policy subfield, a Multi-TID subfield, a Compressed Bitmap subfield, a Reserved subfield, and a TID Information (TID_Info) subfield. It includes.

Table 12 is a table illustrating a BA control field.

The BA Information field includes different information according to the type of the BA frame. This will be described with reference to FIG. 20.

FIG. 20 is a diagram illustrating a BA Information field of a block ACK frame in a wireless communication system to which an embodiment of the present invention may be applied.

20 (a) illustrates a BA Information field of a Basic BA frame, FIG. 20 (b) illustrates a BA Information field of a Compressed BA frame, and FIG. 20 (c) illustrates a BA Information field of a Multi-TID BA frame. To illustrate.

Referring to FIG. 20A, in the case of a Basic BA frame, a BA Information field includes a Block Ack Starting Sequence Control subfield and a Block ACK Bitmap subfield.

The Block Ack Starting Sequence Control subfield includes a Fragment Number subfield and a Starting Sequence Number subfield as described above.

The Fragment Number subfield is set to zero.

The Starting Sequence Number subfield includes the sequence number of the first MSDU for transmitting the corresponding BA frame and is set to the same value as the Basic BAR frame received immediately before.

The Block Ack Bitmap subfield consists of 128 octets and is used to indicate the reception status of up to 64 MSDUs. A value of '1' in the Block Ack Bitmap subfield indicates that the MPDU corresponding to the corresponding bit position was successfully received, and a value of '0' indicates that the MPDU corresponding to the corresponding bit position was not successfully received.

Referring to FIG. 20B, in the case of a compressed BA frame, the BA Information field includes a block ACK starting sequence control subfield and a block ACK bitmap subfield.

The Block Ack Starting Sequence Control subfield includes a Fragment Number subfield and a Starting Sequence Number subfield as described above.

The Fragment Number subfield is set to zero.

The Starting Sequence Number subfield includes the sequence number of the first MSDU or A-MSDU for transmitting the corresponding BA frame, and is set to the same value as the Basic BAR frame received immediately before.

The Block Ack Bitmap subfield is 8 octets long and is used to indicate the reception status of up to 64 MSDUs and A-MSDUs. A value of '1' in the Block Ack Bitmap subfield indicates that a single MSDU or A-MSDU corresponding to the corresponding bit position was successfully received. A value of '0' indicates that a single MSDU or A-MSDU corresponding to the corresponding bit position was successful. Indicates that it has not been received.

Referring to FIG. 20 (c), in the case of a Multi-TID BA frame, a BA Information field may include a Per TID Info subfield, a Block Ack Starting Sequence Control subfield, and a block ACK bit. The Block Ack Bitmap subfield is repeatedly configured for one or more TIDs, and is configured in the order of increasing TIDs.

The Per TID Info subfield includes a reserved subfield and a TID value subfield. The TID Value subfield contains a TID value.

The Block Ack Starting Sequence Control subfield includes the Fragment Number and Starting Sequence Number subfields as described above. The Fragment Number subfield is set to zero. The Starting Sequence Control subfield contains the sequence number of the first MSDU or A-MSDU for which the corresponding BA frame is to be transmitted.

The Block Ack Bitmap subfield consists of 8 octets in length. A value of '1' in the Block Ack Bitmap subfield indicates that a single MSDU or A-MSDU corresponding to the corresponding bit position was successfully received. A value of '0' indicates that a single MSDU or A-MSDU corresponding to the corresponding bit position was successful. Indicates that it has not been received.

Uplink multi-user transmission method

New frames for next-generation WLAN systems, 802.11ax systems, with increasing attention from vendors in various fields for next-generation WiFi and increased demand for high throughput and quality of experience (QoE) after 802.11ac. There is an active discussion of format and numerology.

IEEE 802.11ax is a next-generation WLAN system that supports higher data rates and handles higher user loads. One of the recently proposed WLAN systems is known as high efficiency WLAN (HEW: High). Called Efficiency WLAN).

The IEEE 802.11ax WLAN system may operate in the 2.4 GHz frequency band and the 5 GHz frequency band like the existing WLAN system. It can also operate in the higher 60 GHz frequency band.

In IEEE 802.11ax system, the existing IEEE 802.11 OFDM system (IEEE 802.11a, 802.11n) is used for outdoor throughput transmission for average throughput enhancement and inter-symbol interference in outdoor environment. , 4x larger FFT size for each bandwidth than 802.11ac. This will be described with reference to the drawings below.

Hereinafter, in the description of the HE format PPDU in the present invention, the description of the non-HT format PPDU, the HT-mixed format PPDU, the HT-greenfield format PPDU, and / or the VHT format PPDU described above will be described in HE format unless otherwise noted. May be incorporated into the description of the PPDU.

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

21 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, respectively.

Referring to FIG. 21, 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 that receive 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 includes the same information. In addition, the HE-SIG-A field informs the total bandwidth information of the system.

Table 13 is a table illustrating information included in the HE-SIG A field.

Information included in each field illustrated in Table 12 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. Another embodiment of the information included in the HE-SIG A field will be described later with reference to FIG. 34.

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 (ie, an 80 MHz band), the L-STF, L-LTF, L-SIG, and HE-SIG A fields may be repeatedly transmitted on every 20 MHz channel. .

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.

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

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.

22 illustrates an HE format PPDU according to an embodiment of the present invention.

In FIG. 22, 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. 22, 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. 21, 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 is received by all STAs.

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. 22, the HE-SIG-B may be allocated with 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. 22. 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 addition, unlike the example of FIGS. 21 to 23, 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.

23 illustrates an HE format PPDU according to an embodiment of the present invention.

In FIG. 23, 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. 23, the HE-SIG-B field is not transmitted over the entire band, but is transmitted in 20 MHz units as in 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 information transmitted in each field included in the PPDU is the same as the example of FIG. 21, 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. 29, 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. .

Hereinafter, for convenience of description, the HE format PPDU of FIG. 23 will be described.

21 to 23, the data field is a payload and may include a service field, a scrambled PSDU, tail bits, and padding bits.

Multi-user uplink transmission method

The manner in which an AP operating in a WLAN system transmits data to a plurality of STAs on the same time resource may be referred to as DL MU transmission (downlink multi-user transmission). In contrast, a scheme in which a plurality of STAs operating in a WLAN system transmit data to an AP on the same time resource may be referred to as UL MU transmission (uplink multi-user transmission).

Such DL MU transmission or UL MU transmission may be multiplexed in the frequency domain or the spatial domain.

When multiplexing on the frequency domain, different frequency resources (eg, subcarriers or tones) may be allocated as downlink or uplink resources for each of a plurality of STAs based on orthogonal frequency division multiplexing (OFDMA). Can be. In this same time resource, a transmission scheme using different frequency resources may be referred to as 'DL / UL MU OFDMA transmission'.

When multiplexing on a spatial domain, different spatial streams may be allocated as downlink or uplink resources for each of the plurality of STAs. In this same time resource, a transmission expression through different spatial streams may be referred to as 'DL / UL MU MIMO' transmission.

Current WLAN systems do not support UL MU transmission due to the following limitations.

Current WLAN systems do not support synchronization of transmission timing of uplink data transmitted from a plurality of STAs. For example, assuming that a plurality of STAs transmit uplink data through the same time resource in an existing WLAN system, in the current WLAN system, each of the plurality of STAs may know transmission timing of uplink data of another STA. none. Therefore, it is difficult for the AP to receive uplink data on the same time resource from each of the plurality of STAs.

In addition, in a current WLAN system, overlap between frequency resources used for transmitting uplink data by a plurality of STAs may occur. For example, when oscillators of the plurality of STAs are different, frequency offsets may appear differently. If each of a plurality of STAs having different frequency offsets simultaneously performs uplink transmission through different frequency resources, some of frequency regions used by each of the plurality of STAs may overlap.

In addition, power control for each of the plurality of STAs is not performed in the existing WLAN system. Depending on the distance between the plurality of STAs and the AP and the channel environment, the AP may receive signals of different power from each of the plurality of STAs. In this case, a signal arriving at a weak power may be difficult to be detected by the AP relative to a signal arriving at a strong power.

Accordingly, the present invention proposes a UL MU transmission method in a WLAN system.

24 is a diagram illustrating an uplink multi-user transmission procedure according to an embodiment of the present invention.

Referring to FIG. 24, an AP instructs STAs participating in UL MU transmission to prepare for UL MU transmission, receives UL MU data frames from corresponding STAs, and responds to an UL MU data frame with an ACK frame ( Transmits a Block Ack (BA) frame.

First, the AP transmits a UL MU Trigger frame 2410 to instruct STAs to transmit UL MU data to prepare for UL MU transmission. Here, the UL MU trigger frame may be referred to as a term of a 'UL MU scheduling frame'.

Here, the UL MU trigger frame 2410 may include control information such as STA identifier (ID) / address information, resource allocation information to be used by each STA, duration information, and the like.

The STA ID / address information means information on an identifier or an address for specifying each STA that transmits uplink data.

The resource allocation information is assigned to uplink transmission resources allocated to each STA (for example, frequency / subcarrier information allocated to each STA in case of UL MU OFDMA transmission, and stream index allocated to each STA in case of UL MU MIMO transmission). Means information.

Duration information means information for determining a time resource for transmission of an uplink data frame transmitted by each of a plurality of STAs.

For example, the duration information may include interval information of a TXOP (Transmit Opportunity) allocated for uplink transmission of each STA or information (eg, bits or symbols) about an uplink frame length. Can be.

In addition, the UL MU trigger frame 2410 may further include control information such as MCS information, coding information, etc. to be used when transmitting the UL MU data frame for each STA.

The above control information is the HE-part (eg, HE-SIG A field or HE-SIG B field) of the PPDU carrying the UL MU trigger frame 2410 or the control field (eg, the UL MU trigger frame 2410). For example, the frame control field of the MAC frame) may be transmitted.

The PPDU carrying the UL MU trigger frame 2410 has a structure starting with L-part (eg, L-STF field, L-LTF field, L-SIG field, etc.). Accordingly, legacy STAs may perform Network Allocation Vector (NAV) setting through L-SIG protection from the L-SIG field. For example, legacy STAs may calculate an interval (hereinafter, referred to as an 'L-SIG guard interval') for NAV setting based on data length and data rate information in the L-SIG. The legacy STAs may determine that there is no data to be transmitted to them during the calculated L-SIG protection period.

For example, the L-SIG guard interval may be determined as the sum of the MAC duration field value of the UL MU trigger frame 2410 and the remaining interval after the L-SIG field of the PPDU carrying the UL MU trigger frame 2410. Accordingly, the L-SIG guard period may be set to a value up to a period for transmitting the ACK frame 2430 (or BA frame) transmitted to each STA according to the MAC duration value of the UL MU trigger frame 2410.

Hereinafter, a resource allocation method for UL MU transmission to each STA will be described in more detail. For convenience of description, fields including control information are divided and described, but the present invention is not limited thereto.

The first field may distinguish and indicate UL MU OFDMA transmission and UL MU MIMO transmission. For example, '0' may indicate UL MU OFDMA transmission and '1' may indicate UL MU MIMO transmission. The size of the first field may consist of 1 bit.

The second field (eg, STA ID / address field) informs STA ID or STA addresses to participate in UL MU transmission. The size of the second field may be configured as the number of bits to inform the STA ID × the number of STAs to participate in the UL MU. For example, when the second field consists of 12 bits, the ID / address of each STA may be indicated for every 4 bits.

The third field (eg, resource allocation field) indicates a resource region allocated to each STA for UL MU transmission. In this case, the resource region allocated to each STA may be sequentially indicated to each STA in the order of the second field.

If the first field value is '0', this indicates frequency information (eg, frequency index, subcarrier index, etc.) for UL MU transmission in the order of STA ID / address included in the second field. When the value of the 1 field is '1', it indicates MIMO information (eg, stream index, etc.) for UL MU transmission in the order of STA ID / address included in the second field.

In this case, since a plurality of indexes (ie, frequency / subcarrier indexes or stream indexes) may be informed to one STA, the size of the third field may be configured in a plurality of bits (or bitmap format). × It may be configured as the number of STAs to participate in the UL MU transmission.

For example, it is assumed that the second field is set in the order of 'STA 1' and 'STA 2', and the third field is set in the order of '2', '2'.

In this case, when the first field is '0', STA 1 may be allocated frequency resources from the upper (or lower) frequency domain, and STA 2 may be sequentially allocated the next frequency resource. For example, in case of supporting 20 MHz OFDMA in an 80 MHz band, STA 1 may use a higher (or lower) 40 MHz band, and STA 2 may use a next 40 MHz band.

On the other hand, when the first field is '1', STA 1 may be allocated an upper (or lower) stream, and STA 2 may be sequentially allocated the next stream. In this case, the beamforming scheme according to each stream may be specified in advance, or more specific information about the beamforming scheme according to the stream may be included in the third field or the fourth field.

Each STA transmits UL MU data frames 2421, 2422, and 2423 to the AP based on the UL MU trigger frame 2410 transmitted by the AP. Here, each STA may transmit the UL MU data frames 2421, 2422, 2423 to the AP after SIFS after receiving the UL MU trigger frame 2410 from the AP.

Each STA may determine a specific frequency resource for UL MU OFDMA transmission or a spatial stream for UL MU MIMO transmission based on resource allocation information of the UL MU trigger frame 2410.

Specifically, in the case of UL MU OFDMA transmission, each STA may transmit an uplink data frame on the same time resource through different frequency resources.

Here, each of STA 1 to STA 3 may be allocated different frequency resources for uplink data frame transmission based on STA ID / address information and resource allocation information included in the UL MU trigger frame 2410. For example, STA ID / address information may sequentially indicate STA 1 to STA 3, and resource allocation information may sequentially indicate frequency resource 1, frequency resource 2, and frequency resource 3. In this case, the STA 1 to STA 3 sequentially indicated based on the STA ID / address information may be allocated the frequency resource 1, the frequency resource 2, and the frequency resource 3 sequentially indicated based on the resource allocation information. That is, STA 1 may transmit uplink data frames 2421, 2422, and 2423 to the AP through frequency resource 1, STA 2, frequency resource 2, and STA 3 through frequency resource 3.

In addition, in the case of UL MU MIMO transmission, each STA may transmit an uplink data frame on the same time resource through at least one different stream among a plurality of spatial streams.

Here, each of STA 1 to STA 3 may be allocated a spatial stream for uplink data frame transmission based on STA ID / address information and resource allocation information included in the UL MU trigger frame 2410. For example, STA ID / address information may sequentially indicate STA 1 to STA 3, and resource allocation information may sequentially indicate spatial stream 1, spatial stream 2, and spatial stream 3. In this case, the STA 1 to STA 3 sequentially indicated based on the STA ID / address information may be allocated to the spatial stream 1, the spatial stream 2, and the spatial stream 3 sequentially indicated based on the resource allocation information. That is, STA 1 may transmit uplink data frames 2421, 2422, and 2423 to the AP through spatial stream 1, STA 2, spatial stream 2, and STA 3.

The PPDU carrying the uplink data frames 2421, 2422, and 2423 can be configured in a new structure without the L-part.

In addition, in the case of UL MU MIMO transmission or UL MU OFDMA transmission of subband type of less than 20 MHz, the L-part of the PPDU carrying the uplink data frames 2421, 2422, and 2423 is SFN type (that is, all STAs are the same). L-part configuration and contents can be sent simultaneously). On the other hand, in the case of UL MU OFDMA transmission having a subband type of 20 MHz or more, the L-part of the PPDU carrying the uplink data frames 2421, 2422, and 2423 has a L-part of 20 MHz in the band allocated to each STA. Can be sent.

If the uplink data frame can be sufficiently configured with the information of the UL MU trigger frame 2410, the HE-SIG field in the PPDU carrying the uplink data frames 2421, 2422, and 2423 (that is, how the data frame is constructed). (Area for transmitting the control information) may not be necessary. For example, the HE-SIG-A field and / or the HE-SIG-B may not be transmitted. In addition, the HE-SIG-A field and the HE-SIG-C field may be transmitted, and the HE-SIG-B field may not be transmitted.

The AP may transmit an ACK frame 2430 (or BA frame) in response to the uplink data frames 2421, 2422, and 2423 received from each STA. Here, the AP may receive uplink data frames 2421, 2422, and 2423 from each STA, and transmit an ACK frame 2430 to each STA after SIFS.

If using the same structure of the existing ACK frame, it may be configured to include the AID (or Partial AID) of the STAs participating in the UL MU transmission in the RA field having a size of 6 octets.

Or, if a new structure of the ACK frame can be configured in the form for DL SU transmission or DL MU transmission.

The AP may transmit only the ACK frame 2430 for the UL MU data frame that has been successfully received to the corresponding STA. In addition, the AP may inform whether the reception was successful through the ACK frame 2430 as an ACK or a NACK. If the ACK frame 2430 includes NACK information, the ACK frame 2430 may also include information on the reason for the NACK or information thereafter (eg, UL MU scheduling information).

Alternatively, the PPDU carrying the ACK frame 2430 may be configured in a new structure without the L-part.

The ACK frame 2430 may include STA ID or address information. However, if the order of STAs indicated in the UL MU trigger frame 2410 is applied in the same manner, the STA ID or address information may be omitted.

In addition, the TXOP (that is, the L-SIG guard interval) of the ACK frame 2430 is extended to include a frame for the next UL MU scheduling or a control frame including correction information for the next UL MU transmission. It may be.

Meanwhile, an adjustment process such as synchronization between STAs may be added for UL MU transmission.

Resource allocation

25 through 27 illustrate resource allocation in an OFDMA multi-user transmission scheme according to an embodiment of the present invention.

When a DL / UL OFDMA transmission scheme is used, a plurality of resource units may be defined in units of n tones (or subcarriers) within a PPDU bandwidth.

The resource unit means an allocation unit of frequency resources for DL / UL OFDMA transmission.

One or more resource units may be allocated to one STA as DL / UL frequency resources, and different resource units may be allocated to the plurality of STAs, respectively.

25 illustrates a case where the PPDU bandwidth is 20 MHz.

Seven DC tones may be located in the center frequency region of the 20 MHz PPDU bandwidth. In addition, six left guard tones and five right guard tones may be located at both sides of the 20 MHz PPDU bandwidth.

According to the resource unit configuration method as shown in FIG. 25A, one resource unit may be configured of 26 tones (26 ton resource units). In this case, four leftover tones may be present in the 20 MHz PPDU bandwidth as shown in FIG. 15 (a) adjacent to the 26-tone resource unit. In addition, according to the resource unit configuration method as shown in Fig. 15 (b), one resource unit may be composed of 52 tones (52 ton resource unit) or 26 tones. In this case, four leftover tones may be present in the 20 MHz PPDU bandwidth as shown in FIG. 25 (b) adjacent to the 26 ton / 52 ton resource unit. In addition, according to the resource unit configuration method as shown in FIG. 25 (c), one resource unit may be composed of 106 tones (106 ton resource unit) or 26 tones. In addition, according to the resource unit configuration method as shown in FIG. 25 (d), one resource unit may be configured with 242 tones (242 ton resource unit).

When a resource unit is configured as shown in FIG. 25A, up to nine STAs may be supported for DL / UL OFDMA transmission in a 20 MHz band. In addition, when the resource unit is configured as shown in FIG. 25 (b), up to five STAs may be supported for DL / UL OFDMA transmission in the 20 MHz band. In addition, when the resource unit is configured as shown in FIG. 25 (c), up to three STAs may be supported for DL / UL OFDMA transmission in the 20 MHz band. In addition, when a resource unit is configured as shown in 25 (d), a 20 MHz band may be allocated to one STA.

The resource unit configuration method of FIG. 25 (a) to FIG. 25 (d) may be applied based on the number of STAs participating in DL / UL OFDMA transmission and / or the amount of data transmitted or received by the STA. Alternatively, the resource unit configuration scheme in which FIGS. 25A to 25D are combined may be applied.

FIG. 26 exemplifies a case where the PPDU bandwidth is 40 MHz.

Five DC tones may be located in the center frequency region of the 40 MHz PPDU bandwidth. In addition, 12 left guard tones and 11 light guard tones may be located at both sides of the 40 MHz PPDU bandwidth.

According to the resource unit configuration method as shown in FIG. 26 (a), one resource unit may consist of 26 tones. In this case, 16 leftover tones may be present in the 40 MHz PPDU bandwidth as shown in FIG. 16 (a) adjacent to the 26-tone resource unit. In addition, according to the resource unit configuration method as shown in FIG. 26 (b), one resource unit may consist of 52 tones or 26 tones. In this case, 16 leftover tones may be present in the 40 MHz PPDU bandwidth as shown in FIG. 16 (b) adjacent to the 26 ton / 52 ton resource unit. In addition, according to the resource unit configuration method as shown in FIG. 26C, one resource unit may be configured of 106 tones or 26 tones. In this case, eight leftover tones may be present in the 40 MHz PPDU bandwidth as shown in FIG. 16 (c) adjacent to the 26 tone / 106 tone resource unit. In addition, according to the resource unit configuration method as shown in FIG. 26 (d), one resource unit may be configured with 242 tones. In addition, according to the resource unit configuration method as shown in FIG. 26E, one resource unit may be configured of 484 tones (484 ton resource unit).

When a resource unit is configured as shown in FIG. 26A, up to 18 STAs may be supported for DL / UL OFDMA transmission in a 40 MHz band. In addition, when a resource unit is configured as shown in FIG. 26 (b), up to 10 STAs may be supported for DL / UL OFDMA transmission in a 40 MHz band. In addition, when a resource unit is configured as shown in FIG. 26C, up to six STAs may be supported for DL / UL OFDMA transmission in a 40 MHz band. In addition, when the resource unit is configured as shown in 26 (d), up to two STAs may be supported for DL / UL OFDMA transmission in the 40 MHz band. In addition, when a resource unit is configured as shown in 26 (e), the corresponding resource unit may be allocated to one STA for SU DL / UL transmission in the 40 MHz band.

The resource unit configuration method of FIG. 26 (a) to FIG. 26 (e) may be applied based on the number of STAs participating in DL / UL OFDMA transmission and / or the amount of data transmitted or received by the STA. Alternatively, the resource unit configuration scheme in which FIGS. 26 (a) to 26 (e) are combined may be applied.

27 illustrates a case where the PPDU bandwidth is 80 MHz.

Seven DC tones may be located in the center frequency region of the 80 MHz PPDU bandwidth. However, when 80 MHz PPDU bandwidth is allocated to one STA (that is, when a resource unit composed of 996 tones is allocated to one STA), five DC tones may be located in the center frequency region. In addition, 12 left guard tones and 11 light guard tones may be located at both sides of the 80 MHz PPDU bandwidth.

According to the resource unit configuration method as shown in FIG. 27 (a), one resource unit may consist of 26 tones. In this case, 32 leftover tones may be present in the 80 MHz PPDU bandwidth as shown in FIG. 27 (a) adjacent to the 26-tone resource unit. In addition, according to the resource unit configuration method as shown in FIG. 27B, one resource unit may be composed of 52 tones or 26 tones. In this case, 32 leftover tones may be present in the 80 MHz PPDU bandwidth as shown in FIG. 27 (b) adjacent to the 26 tone / 52 tone resource unit. In addition, according to the resource unit configuration method as shown in FIG. 27C, one resource unit may include 106 tones or 26 tones. In this case, 16 leftover tones may be present in the 80 MHz PPDU bandwidth as shown in FIG. 27 (c) adjacent to the 26 tone / 106 tone resource unit. In addition, according to the resource unit configuration method as shown in FIG. 27 (d), one resource unit may be configured of 242 tones or 26 tones. According to the resource unit configuration method as shown in FIG. 27 (e), one resource unit may consist of 484 tones or 26 tones. According to the resource unit configuration method as shown in FIG. 17 (f), one resource unit may consist of 996 tones.

When a resource unit is configured as shown in FIG. 27A, up to 37 STAs may be supported for DL / UL OFDMA transmission in an 80 MHz band. In addition, when the resource unit is configured as shown in FIG. 27 (b), up to 21 STAs may be supported for DL / UL OFDMA transmission in the 80 MHz band. In addition, when a resource unit is configured as shown in FIG. 27C, up to 13 STAs may be supported for DL / UL OFDMA transmission in an 80 MHz band. In addition, when the resource unit is configured as shown in 27 (d), up to five STAs may be supported for DL / UL OFDMA transmission in the 80 MHz band. In addition, when the resource unit is configured as shown in 27 (e), up to three STAs may be supported for DL / UL OFDMA transmission in the 80 MHz band. In addition, when a resource unit is configured as shown in 27 (f), the corresponding resource unit may be allocated to one STA for SU DL / UL transmission in the 80 MHz band.

The resource unit configuration method of FIG. 27 (a) to FIG. 27 (f) may be applied based on the number of STAs participating in DL / UL OFDMA transmission and / or the amount of data transmitted or received by the STA. Alternatively, the resource unit configuration scheme in which FIGS. 27 (a) to 27 (f) are combined may be applied.

In addition, although not shown in the figure, a configuration method of a resource unit when the PPDU bandwidth is 160 MHz may be proposed. In this case, the bandwidth of the 160MHz PPDU may have a structure in which the 80MHz PPDU bandwidth described above in FIG. 27 is repeated twice.

Only some resource units may be used for DL / UL OFDMA transmission among all resource units determined according to the above-described resource unit configuration. For example, when resource units are configured as shown in FIG. 27A within 20 MHz, one resource unit may be allocated to less than nine STAs, and the remaining resource units may not be allocated to any STAs.

In the case of DL OFDMA transmission, the data field of the PPDU is multiplexed and transmitted in a frequency domain in units of resource units allocated to each STA.

On the other hand, in the case of UL OFDMA transmission, the data field of the PPDU may be configured in units of resource units allocated to each STA and transmitted simultaneously to the AP. As described above, since each STA simultaneously transmits a PPDU, it may be recognized that a data field of a PPDU transmitted from each STA is multiplexed (or frequency multiplexed) in the frequency domain from the viewpoint of the AP.

In addition, when DL / UL OFDMA transmission and DL / UL MU-MIMO transmission are simultaneously supported, one resource unit may consist of a plurality of streams in a spatial domain. In addition, one or more streams may be allocated to one STA as DL / UL spatial resources, and different streams may be allocated to the plurality of STAs, respectively.

For example, a resource unit composed of 106 tones in FIG. 27C may be configured of a plurality of streams in a spatial domain to simultaneously support DL / UL OFDMA and DL / UL MU-MIMO.

Hereinafter, for convenience of description, a resource unit composed of n tones will be referred to as an 'n tone resource unit' (n is a natural number). For example, in the following, a resource unit consisting of 26 tones is referred to as a '26 ton resource unit '.

Resource request and UL MU transmission method

As described above, the STAs may transmit a resource request to the AP for DL MU transmission. The AP transmits a buffer status request or a buffer status report request to the STAs that have received the resource request, and allocates resources to the STAs based on the received buffer status report / information. Can be. STAs to which resources are allocated may initiate UL MU transmission based on the allocated resources.

The resource request transmitted by the STA and the buffer status request of the AP may be included in the HE control field of the trigger frame or the MAC header to be transmitted and received. The resource allocation information and the buffer status report may be included in the MAC header or the MAC payload and transmitted. Resource request and resource allocation may also be referred to below as resource request and resource allocation.

28 illustrates a resource request method according to an embodiment of the present invention.

28 shows a PHY resource request scheme using a HE-LTF sequence. In an embodiment of the present invention, the resource request may consist of a signal frame as shown in FIG. Long Traning Field (HE-LTF) provides a means for MIMO channel estimation between the receiver chain of the receiver and the constellation mapper output of the transmitter (or the STBC encoder output in STBC application).

As an embodiment of the present invention, we propose a method for a STA to transmit a resource request to an AP using a HE-LTF sequence. As illustrated in FIG. 25, nine resource units are included in the 20 MHz bandwidth. Four or eight spatial streams may be transmitted at 20 MHz. Therefore, if the 20 MHz band is allocated to a combination of resource units and spatial streams, the 20 MHz band is allocated to 36 STAs in a combination of 9 resource units and 4 streams or 72 STAs in a combination of 9 resource units and 8 streams. Can be.

In FIG. 28, the STA may transmit using the L-SIG field, the HE-SIG-A field, and the HE-STF using 20 MHz bands. The STA may perform the resource request by using the specific resource unit for the HE-LTF or transmitting the HE-LTF using the specific resource unit and spatial multiplexing. The signal including the L-SIG field, the HE-SIG-A field, the HE-STF field, and the HE-LTF field occupying at least one resource unit may be referred to as a resource request signal or a resource request frame.

As an embodiment, when the STA receives a signal such as a beacon frame, a trigger frame, etc., the STA may transmit a resource request signal in response thereto. The resource request signal may be transmitted in a UL MU scheme.

The resource request signal may be transmitted with random access or may be assigned in advance. The AP may signal to the STAs which STA to allocate each HE-LTF region to. If the STA transmits the HE-LTF to the allocated HE-LTF area, there is a resource request. If the STA does not transmit, there is no resource request. In the resource request signal, the STA may transmit 20 MHz from the legacy preamble portion to the HE-STF in common. As an embodiment, the STA may perform the resource request by omitting the legacy preamble portion and transmitting the HE-STA and the HE-LTF.

The AP receiving the resource request may transmit an ACK signal. The AP may allocate a UL MU frame to STAs by transmitting a trigger frame for transmitting UL MU data.

When using the physical resource request signal as shown in FIG. 28, the AP may receive and acquire the resource request signal very quickly. Since the presence or absence of the HE-LTF can immediately determine whether a specific AP resource request, there is an advantage that the AP can quickly respond to the resource request of a plurality of STAs.

 The AP, which has received the resource request signal of the embodiment of FIG. 28, may know that a specific STA needs resource allocation, but other information may not be known, and thus, it is difficult to immediately transmit a trigger frame by allocating an appropriate resource. That is, in the embodiment of FIG. 28, since the resource request signal indicates only that a specific STA needs resource allocation, the AP may request and receive a buffer status report and allocate resources accordingly. Hereinafter, a subsequent operation of receiving a buffer status report and transmitting a trigger frame after receiving a resource request signal will be described.

29 illustrates a method of resource allocation and UL MU reception according to an embodiment of the present invention.

The AP may transmit resource unit allocation information 29010 to transmit the HE-LTF for the resource request. As described in FIG. 28, the AP may allocate a combination of resource units and spatial multiplexing to 9 to 72 STAs for each 20MHz bandwidth. Accordingly, in the case of the 160 MHz band, resource units may be allocated to 9 * 8 STAs or a combination of resource units and spatial multiplexing may be allocated to 72 * 8 STAs.

29 shows an embodiment of allocating a specific resource unit or resource unit and spatial stream to STAs. The AP may transmit resource unit allocation information 29010 and may further transmit a signal for initiating UL MU transmission of the resource request, such as an additional beacon frame or a trigger frame. The resource unit allocation information 29010 that the AP transmits may include information about a resource unit or a combination of resource units and spatial streams to which the respective STAs transmit the HE-LTF for the resource request.

An STA having data to be UL may transmit a resource request 29020 using the allocated resource unit. In the embodiment of FIG. 29, STA1 to STA4 and STA11 may transmit the HE-LTF 29020 through the allocated resource unit or through the allocated resource unit and the allocated spatial stream, respectively. The embodiment of FIG. 29 is an embodiment of mapping a specific resource unit to a specific STA and allocating the same. Therefore, the AP that has received the resource request can immediately identify the transmitting STA by the resource unit location / spatial stream number of the resource request.

The AP may transmit an ACK frame 29030 when receiving the resource request. However, the transmission of the ACK signal 2902 at this stage may be omitted to simplify the communication procedure and reduce overhead.

The AP may transmit a buffer status request 29040 requesting to send a buffer status report. The AP may transmit a request signal / frame 29040 of the buffer status report using the resource unit receiving the resource request. The frame transmitted for the buffer status request 29040 may be a broadcast trigger frame, a unicast trigger frame, or a trigger frame for random access. The buffer status request 29040 may include trigger information for receiving a buffer status report to the UL MU.

The STA may transmit a buffer status report 29050 in response to the buffer status request of the AP. The buffer status report may be referred to as buffer status information. The buffer status report 29050 may be sent as a MAC frame. The buffer status report 29050 may include a buffer size, access category (AC) information, and the like. The buffer status report 29050 is transmitted in a UL MU manner, and thus the buffer status request may include trigger information for specifying a transmission area. Trigger information for UL MU reception of the buffer status report 29050 may be included in the buffer status request signal / frame or transmitted in a separate frame. A buffer status request for a plurality of STAs may also be transmitted.

The AP may send an ACK frame 29060 upon receiving the buffer status report. However, the transmission of the ACK signal 29060 at this stage may be omitted to simplify the communication procedure and reduce overhead.

The AP may send available UL resource scheduling as the trigger frame 29070 based on resource requests of the STAs. In addition, the plurality of STAs that receive the trigger frame may transmit the UL MU frame 29080. The trigger frame 29070 transmission of the AP and the UL MU frame 29080 transmission of the STAs may be performed as described with reference to FIG. 24. Although not shown in FIG. 29, the AP receiving the UL MU frame 29080 may transmit an ACK frame to the STAs.

In FIG. 29, when there is no dotted line between frames, a signal / frame is transmitted after a time interval such as SIFS, and when there is a dotted line, a frame is transmitted after an SIFS time interval or an enhanced distributed channel access (EDCA) competition ( frame after contention). For example, the AP may transmit a frame / signal through EDCA competition after further gathering information on other STAs. As an embodiment, the operation of Phase 2 / Phase 3 may be performed after the operation of Phase 1 is performed a plurality of times, or the operation of Phase 3 may be performed after the operations of Phase 1 and Phase 2 are performed a plurality of times. .

The embodiment of FIG. 29 may request / receive a buffer status report directly from an STA that has transmitted a resource request, and thus, additional resource allocation for the buffer status report is unnecessary. Therefore, unnecessary resource occupation can be reduced. Since STAs do not need to additionally transmit their STA IDs, the communication procedure can be simplified.

30 illustrates a resource allocation and a UL MU reception method according to an embodiment of the present invention.

The AP may transmit resource unit allocation information 30010 to transmit the HE-LTF for the resource request. However, unlike FIG. 29, FIG. 30 illustrates an embodiment of allocating resources by a random access method.

As described with reference to FIG. 28, the AP may allocate resource units or a combination of resource units and spatial multiplexing to 9 to 72 STAs for each 20MHz bandwidth. Accordingly, in the case of the 160 MHz band, resource units may be allocated to 72 STAs or a combination of resource units and spatial multiplexing may be allocated to 576 STAs.

In the embodiment of FIG. 30, the resource unit allocation information 30010 may indicate only a resource allocation scheme, not resource allocation information for each STA. In an embodiment, the resource unit allocation information 30010 may indicate a configuration method of the HE-LTF region (for example, nine resource units * 8 spatial streams). That is, the resource unit allocation information 30010 indicates a resource unit allocation method for resource request or a combination method of resource unit and spatial multiplexing, and the STA may randomly select one of them and transmit the HE-LTF to the corresponding region.

The AP may transmit resource request allocation information 30010 and may further transmit a signal for starting resource request transmission, such as a beacon frame and a trigger frame.

An STA having data to be UL may transmit a resource request 30020 based on resource allocation information. In the embodiment of FIG. 30, the STA may transmit the HE-LTF sequence 30020 to a region randomly selected from among the HE-LTF slots. FIG. 30 illustrates an embodiment in which STAs 1 to 4 and STA 11 select regions of HE- LTF 5 and 20 to 23 to transmit a HE-LTF sequence, respectively. In this case, the HE-LTF numbers are randomly numbered according to the number of RUs and the number of spatial streams.

When the AP receives the resource request, the AP may transmit an ACK frame 30030. However, transmission of the ACK signal 30030 in this step may be omitted to simplify the communication procedure and reduce overhead.

The AP may transmit a buffer status request signal / frame 30040 requesting to transmit a buffer status report. Since the AP does not yet know the STA information that transmitted the resource request, the AP may transmit the buffer status request 30040 by using the resource unit that received the resource request. That is, the STA detects the HE-LTF area and signals the HE-LTF number of the received area, and may transmit a buffer status request to transmit a buffer status report to the STAs transmitted to the corresponding HE-LTF number.

The frame 30040 carrying the buffer status request information may be a broadcast trigger frame, a unicast trigger frame, or a trigger frame for random access. The buffer status request signal / frame 30040 may include trigger information for receiving a buffer status report to the UL MU.

The STA may transmit a buffer status report 30050 in response to the buffer status request of the AP. Buffer status report 30050 may be sent as a MAC frame. The buffer status report 30050 may include STA ID information, buffer size, and access category (AC) information. In the embodiment of FIG. 30, since the AP has not yet identified the STA that has transmitted the resource request, the STA must transmit its own identification information in the buffer status report. The buffer status report 30050 is transmitted in a UL MU manner, and thus the buffer status request may include trigger information for specifying a transmission area. Trigger information for UL MU reception of the buffer status report 30050 may be included in the buffer status request signal / frame or transmitted in a separate frame. A buffer status request for a plurality of STAs may also be transmitted.

In the embodiment of FIG. 30, since the HE-LTF is not allocated in advance, an overhead of resource allocation information may be reduced. In particular, when the number of STAs that the AP communicates with is not large, it may be efficient to reduce unnecessary prior procedures and use the embodiment of FIG. 30.

The AP may send an ACK frame 30060 upon receiving the buffer status report. However, the transmission of the ACK signal 30060 at this stage may be omitted to simplify the communication procedure and reduce overhead.

The AP may send available UL resource scheduling as the trigger frame 30070 based on resource requests of the STAs. In addition, the plurality of STAs that receive the trigger frame may transmit the UL MU frame 30080. Transmission of the trigger frame 30070 of the AP and UL MU frame 30080 of the STAs may be performed as described with reference to FIG. 24. Although not shown in FIG. 30, the AP receiving the UL MU frame 30080 may transmit an ACK frame to the STAs.

In FIG. 30, when there is no dotted line between frames, a signal / frame is transmitted after a time interval such as SIFS, and when there is a dotted line, a frame is transmitted after an SIFS time interval or an enhanced distributed channel access (EDCA) competition ( frame after contention). For example, the AP may transmit a frame / signal through EDCA competition after further gathering information on other STAs. As an embodiment, the operation of Phase 2 / Phase 3 may be performed after the operation of Phase 1 is performed a plurality of times, or the operation of Phase 3 may be performed after the operations of Phase 1 and Phase 2 are performed a plurality of times. .

31 is a flowchart illustrating a UL MU transmission method of an STA apparatus according to an embodiment of the present invention.

The above-described embodiments can be equally applied to the description related to the present flowchart. Therefore, hereinafter, redundant descriptions may be omitted.

The STA may transmit a resource request (S31010). The resource request may be transmitted in the form of a signal as shown in FIG. 28. That is, the resource request may correspond to a signal frame including an HE-LTF sequence occupying a specific resource unit.

The STA may receive resource unit allocation information for resource request transmission in advance. The resource unit allocation information may indicate a specific resource unit or a combination of a specific spatial unit and a specific spatial multiplexing to which the STA sends a resource request. Alternatively, the resource unit allocation information may indicate configuration information on a resource unit or a combination of resource units and spatial multiplexing. Accordingly, the STA may transmit a resource request by using a combination of a specific resource unit or a specific resource unit and a specific spatial multiplexing or transmit a resource request by using a randomly selected combination of a resource unit or a resource unit and a spatial multiplexing.

The STA may receive a buffer status request (S31020). The buffer status request may include trigger information for UL MU transmission of the buffer status information. The buffer status request may be received through a resource unit to which the STA has sent a resource request, or may be received through a combination of spatial multiplexing with the resource unit which has transmitted the resource request.

The STA may transmit buffer status information (S31030). The buffer status information may indicate the amount of traffic queued in the STA's buffer. The buffer state information may be included in the MAC frame of the transmission data as the queue size subfield of the QoS control field or the HE-A-control field. The buffer status information may indicate the status of access category (AC) buffers in a TDLS Peer U-PASD (TPU) buffer STA. When the STA uses a randomly selected resource unit or a combination of resource multiplexing and spatial multiplexing when transmitting a resource request, the buffer state information may include information for identifying the STA. In an embodiment, the information for identifying the STA may be a STA ID.

The STA may receive trigger information (S31040). The trigger information may include resource unit allocation information for UL MU frame transmission and length information of the UL MU frame. The resource unit allocation information of the trigger information may indicate the resource unit allocated by the AP based on the buffer state transmitted by the STA.

The STA may transmit a UL MU frame (S31050). The UL MU frame may correspond to a UL MU PPDU. The STA may transmit a UL MU frame including at least one resource unit using an OFDMA scheme. The STA may transmit data to at least one resource unit indicated by the trigger information. That is, the STA may transmit a UL MU frame in which the data portion occupies at least one resource unit. The STA transmits a UL MU PPDU based on the received trigger information.

32 is a block diagram of each STA apparatus according to an embodiment of the present invention.

In FIG. 31, the STA apparatus 32000 may include a memory 32010, a processor 32020, and an RF unit 32030. As described above, the STA device may be an AP or a non-AP STA as an HE STA device.

The RF unit 32030 may be connected to the processor 32020 to transmit / receive a radio signal. The RF unit 32030 may up-convert data received from the processor 32020 into a transmission / reception band to transmit a signal.

The processor 32020 may be connected to the RF unit 32030 to implement a physical layer and / or a MAC layer according to the IEEE 802.11 system. The processor 32020 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, a module implementing the operation of the STA 32000 according to various embodiments of the present disclosure described above may be stored in the memory 32010 and executed by the processor 32020.

The memory 32010 is connected to the processor 32020 and stores various information for driving the processor 32020. The memory 32010 may be included in the processor 32020 or may be installed outside the processor 32020 and connected to the processor 32020 by known means.

In addition, the STA apparatus 32000 may include a single antenna or multiple antennas.

The specific configuration of the STA apparatus 32000 of FIG. 32 may be implemented such that the above-described matters described in various embodiments of the present invention are applied independently or two or more embodiments are simultaneously applied.

In the method of transmitting UL MU data of the STA apparatus 32000 illustrated in FIG. 32, not only the description related to the flowchart of FIG. 31 but also the description of the above specification may be applied.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in memory and driven by the processor. The memory may be located inside or outside the processor, and may exchange data with the processor by various known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

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

The frame transmission scheme in the wireless communication system of the present invention 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 (12)

1. In a wireless LAN (WLAN) system, an uplink (UL) multi-user (MU) transmission method of a STA (Station) device,

   Transmitting a resource request to an access point (AP);

   Receiving a buffer status request from the AP;

   Transmitting buffer status information to the AP;

   Receiving trigger information for UL MU transmission from the AP;

   And transmitting an UL MU frame including at least one resource unit based on the trigger information by using an orthogonal frequency division multiple access (OFDMA) scheme.
2. The method of claim 1,

   The trigger information, the UL MU transmission method including resource unit allocation (Resource Unit Allocation) information and the length information of the UL MU frame for the UL MU frame transmission.
3. The method of claim 1,

   The buffer status information indicates the amount of queued traffic of the STA device.
4. The method of claim 1,

   And the resource request is a signal frame including a High Efficiency (HE) -Long Training Field (LTF) sequence occupying a specific resource unit.
5. The method of claim 4, wherein

   And receiving resource unit allocation information indicating allocation of the resource unit to send the resource request.
6. The method of claim 4, wherein

   The buffer status request is received via the specific resource unit to which the resource request was sent.
7. In the STA (Station) device in a wireless LAN (WLAN) system,

   An RF unit for transmitting and receiving wireless signals; And

   A processor for controlling the RF unit,

   The STA device,

   Sends a resource request to an access point (AP),

   Receiving a buffer status request from the AP,

   Transmit buffer status information to the AP,

   Receive trigger information for UL MU transmission from the AP,

   And a UL MU frame including at least one resource unit based on the trigger information using an orthogonal frequency division multiple access (OFDMA) scheme.
8. The method of claim 7, wherein

   The trigger information includes a resource unit allocation (Resource Unit Allocation) information and the length information of the UL MU frame for the UL MU frame transmission.
9. The method of claim 7, wherein

   Wherein the buffer status information indicates the amount of queued traffic of the STA device.
10. The method of claim 7, wherein

    And the resource request is a signal frame including a High Efficiency (HE) -Long Training Field (LTF) sequence that occupies a specific resource unit.
11. The method of claim 10,

    STA unit, receiving resource unit allocation information indicating allocation of the resource unit to transmit the resource request.
12. The method of claim 10,

    And the buffer status request is received via the specific resource unit to which the resource request was sent.

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