KR20150118897A - Method for beamforming feedback by wireless local area network device - Google Patents

Abstract

A method for beamforming feedback of a device in a wireless local area network includes the steps of: receiving a first frame from a transmission device to which beamforming data is expected to be transmitted; estimating a normal direction channel on the basis of the first frame; calculating a beamforming feedback matrix from the normal direction channel; and transmitting a second frame including the beamforming feedback matrix to the transmission device.

Description

METHOD FOR BEAMFORMING FEEDBACK BY WIRELESS LOCAL AREA NETWORK DEVICE [0001]

The present invention relates to a beamforming feedback method, and more particularly to a beamforming feedback method in a wireless local area network (WLAN) (hereinafter referred to as "wireless LAN").

Wireless LANs are being standardized under the name of "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications" in IEEE P11. The IEEE 802.11a standard (IEEE Std 802.11a-1999), which supports the 2.4 GHz band, was released in 1999, and the IEEE Std 802.11g-2003, which supports the 5 GHz band in 2003, These standards are called legacy. The IEEE 802.11n standard (IEEE Std 802.11n-2009) for higher throughput (HT) was released in 2009, and the IEEE 802.11ac standard for very high throughput (VHT) enhancement IEEE 802.11ac-2013) was released in 2013. Currently, the IEEE 802.11ax task group is developing a high efficiency WLAN (HEW) that can improve system throughput in high density environments.

Single User-Multiple Input and Multiple Output (SU-MIM0) and Multiple User-Multiple Input and Multiple Output (MU-MIMO) have been introduced in the IEEE 802.11ac standard. SU-MIMO utilizes channel feedback based transmission beamforming to obtain higher data rates in the same channel environment. MU-MIMO is a technique that an access point (AP) simultaneously transmits a plurality of frames to a plurality of terminals on the same channel, and can simultaneously transmit to a plurality of terminals using feedback-based transmission beamforming. The transmission beamforming and the downlink MU-MIMO require channel state information to calculate the beamforming information applied to a signal transmitted to the UE, i.e., a steering matrix. The AP may receive channel state information from the terminal through an explicit feedback mechanism of the sounding protocol. When the AP transmits a sounding frame including a training symbol to the terminal, the terminal quantizes and feeds back channel information estimated based on the training symbol. When a terminal transmits a Compressed Beamforming (CB) frame, the AP performs beamforming based on feedback information received from the terminal.

As such, the feedback frame is exchanged before data transmission to optimize the data transmission signal. However, as the feedback information is quantized, the amount of data increases considerably. In some cases, the size of the feedback information may exceed the size of the MAC Protocol Data Unit (MPDU). As a result, considerable time is required before the data frame due to the overhead of the feedback frame. Therefore, when the channel variation is large or the transmission data is not large, the beam forming efficiency is limited.

SUMMARY OF THE INVENTION The present invention provides a beamforming feedback method for a wireless LAN device.

A beamforming feedback method of a device in a wireless local area network (WLAN) in accordance with an embodiment of the present invention includes receiving a first frame from a transmitting device that is scheduled to transmit beamforming data, Estimating a channel, calculating a beamforming feedback matrix from the forward channel, and transmitting a second frame including the beamforming feedback matrix to the transmitting device.

The transmitting of the second frame inserts the beamforming feedback matrix into the feedback field of the second frame, and the feedback field may be located between the training field and the data field of the second frame.

The step of transmitting the second frame may transmit the information of the training field and the feedback field on a sub-carrier of each antenna.

The beamforming feedback method may further include inserting SINR information of a subcarrier into a signal field or a data field of the second frame.

Wherein the beamforming feedback method further comprises receiving an acknowledgment frame informing of the first frame transmission from the transmitting device prior to receiving the first frame, wherein the acknowledgment frame includes an indicator for requesting beamforming feedback matrix transmission can do.

The beamforming feedback matrix may be a unitary matrix, and the step of calculating the beamforming feedback matrix may calculate the unitary matrix by singular value decomposition of the forward channel.

A beamforming feedback method of a device in a wireless local area network (WLAN), according to another embodiment of the present invention, includes transmitting a first frame to a receiving device that is scheduled to receive beamforming data, Estimating a reverse channel based on the second frame, and equalizing the reverse channel to extract the analog feedback information in the second frame.

The analog feedback information may be included in a feedback field of the second frame and the feedback field may be located between a training field and a data field of the second frame.

The step of extracting the analog feedback information may calculate the analog feedback information by equalizing the reverse channel in a signal related to the feedback field of the received signal.

The analog feedback information may be a beamforming feedback matrix.

The beamforming feedback method may further include beamforming a data frame using the extracted beamforming feedback matrix.

The analog feedback information may be a forward channel matrix estimated by the receiving device.

The beamforming feedback method may further include a step of calculating a beamforming feedback matrix by singular value decomposition of the extracted forward channel matrix and beamforming a data frame using the beamforming feedback matrix have.

Wherein the beamforming feedback method further comprises transmitting, before the first frame transmission, a notification frame informing the receiving device of the first frame transmission, the notification frame including a feedback mode indicator, May include analog feedback information corresponding to the feedback mode indicator.

A beamforming feedback method of a device in a wireless local area network (WLAN) according to another embodiment of the present invention includes transmitting a Null Data Packet Announcement (NDPA) frame indicating a feedback mode to a receiving device, Transmitting a Null Data Packet (NDS) frame to the base station, and receiving a feedback frame including feedback information generated according to the feedback mode.

The feedback mode may include a first mode for quantizing and feeding back a channel to angle information, a second mode for feeding back a beamforming feedback matrix, and a third mode for feeding back the estimated channel matrix.

If the NDPA frame indicates the second mode, the feedback frame may include a beamforming feedback matrix in the feedback field, and the feedback field may be located between the training field and the data field of the feedback frame.

The beamforming feedback method may further include estimating an uplink channel based on the feedback frame, and equalizing the uplink channel to extract the beamforming feedback matrix in the feedback frame.

If the NDPA frame indicates the third mode, the feedback frame includes a forward channel matrix estimated at the receiving device in the feedback field, and the feedback field is located between the training field and the data field of the feedback frame .

The beamforming feedback method comprises the steps of estimating an uplink channel based on the feedback frame, equalizing the uplink channel and extracting the forward channel matrix from the feedback frame, and converting the extracted forward channel matrix into a singular value decomposing the beamforming feedback matrix to calculate a beamforming feedback matrix.

According to an embodiment of the present invention, a beamforming feedback matrix may be transmitted as analog data to reduce overhead due to quantization, and beamforming efficiency may be increased. According to an embodiment of the present invention, it can be applied even in a situation where beamforming is not used due to overhead burden of a conventional feedback frame. According to an exemplary embodiment of the present invention, an optimum feedback method can be selected from among various feedback methods according to a channel state, transmission data size, and the like.

1 is a schematic block diagram illustrating the structure of a wireless LAN device.
2 is a schematic block diagram illustrating a transmission signal processing unit in a wireless LAN.
3 is a schematic block diagram illustrating a received signal processing unit in a wireless LAN.
4 is a diagram showing an interframe space (IFS) relationship.
5 is an illustration of frame exchange of a Single User-Beamforming (SU-BF).
6 is an illustration of frame exchange of Multiple User-Beamforming (MU-BF).
7 is an exemplary diagram illustrating a beamforming feedback method according to an embodiment of the present invention.
8 is an exemplary diagram illustrating a beamforming feedback method according to another embodiment of the present invention.
9 is a flow diagram of a method of feedbacking a beamforming feedback matrix in accordance with an embodiment of the present invention.
10 is a flowchart of a method of feeding back an estimated channel matrix according to another embodiment of the present invention.
11 is a diagram showing an NDPA MAC frame in a wireless LAN.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

A basic service set (BSS) in a wireless local area network (WLAN) (hereinafter referred to as a "wireless LAN") includes a plurality of wireless LAN devices. The WLAN device may include a medium access control (MAC) layer and a physical (PHY) layer according to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. At least one of the plurality of wireless LAN devices may be an access point (AP), and the remaining wireless LAN device may be a non-AP station (non-AP STA). Or ad-hoc networking, a plurality of wireless LAN devices may all be non-AP stations. In general, a station (STA) is also used when collectively referred to as an access point (AP) and a non-AP station, but for simplicity, the non-AP station is also abbreviated as a station (STA).

1 is a schematic block diagram illustrating the structure of a wireless LAN device.

1, the wireless LAN device 1 includes a baseband processor 10, a radio frequency (RF) transceiver 20, an antenna unit 30, a memory 40, an input interface unit 50, An output interface unit 60 and a bus 70. Fig.

The baseband processor 10 performs the baseband-related signal processing described herein, and includes a MAC processor 11, a PHY processor 15, and the like.

In one embodiment, the MAC processor 11 may include a MAC software processing unit 12 and a MAC hardware processing unit 13. At this time, the memory 40 includes software (hereinafter referred to as "MAC software") including some functions of the MAC layer, and the MAC software processing unit 12 implements some functions of the MAC by driving the MAC software, The MAC hardware processing unit 13 may implement the remaining functions of the MAC layer as hardware (hereinafter referred to as "MAC hardware"), but is not limited thereto.

The PHY processor 15 includes a transmission signal processing unit 100 and a reception signal processing unit 200.

The baseband processor 10, the memory 40, the input interface unit 50 and the output interface unit 60 can communicate with each other via the bus 70. [

The RF transceiver 20 includes an RF transmitter 21 and an RF receiver 22.

In addition to the MAC software, the memory 40 may store an operating system, an application, etc., and the input interface unit 50 acquires information from the user, and the output interface unit 60 acquires information from the user Output.

The antenna section 30 includes one or more antennas. When using multiple-input multiple-output (MIMO) or multi-user MIMO (MU-MIMO), the antenna unit 30 may include a plurality of antennas.

2 is a schematic block diagram illustrating a transmission signal processing unit in a wireless LAN.

2, the transmission signal processing unit 100 includes an encoder 110, an interleaver 120, a mapper 130, an inverse Fourier transformer 140, and a guard interval (GI) inserter 150 do.

Encoder 110 encodes the input data and may be, for example, a forward error correction (FEC) encoder. The FEC encoder may include a binary convolutional code (BCC) encoder, in which case a puncturing device may be included. Or the FEC encoder may include a low-density parity-check (LDPC) encoder.

The transmission signal processing unit 100 may further include a scrambler scrambling the input data before encoding the input data to reduce the probability that a long same sequence of 0's or 1's occurs. If a plurality of BCC encoders are used as the encoder 110, the transmission signal processing unit 100 may further include an encoder parser for demultiplexing the scrambled bits into a plurality of BCC encoders. When an LDPC encoder is used as the encoder 110, the transmission signal processing unit 100 may not use the encoder parser.

The interleaver 120 interleaves the bits of the stream output from the encoder 110 to change the order. Interleaving may be applied only when a BCC encoder is used as the encoder 110. [ The mapper 130 maps the bit stream output from the interleaver 120 to constellation points. When an LDPC encoder is used as the encoder 110, the mapper 130 may perform LDPC tone mapping in addition to the property store mapping.

When SU-MIMO or MU-MIMO is used, the transmission signal processing unit 100 can use a plurality of interleavers 120 and a plurality of mappers 130 corresponding to the number of spatial streams N _SS have. The transmission signal processing unit 100 may further include a stream parser that divides outputs of a plurality of BCC encoders or LDPC encoders into a plurality of blocks to be provided to different interleavers 120 or a mapper 130. The transmission signal processing unit 100 further includes a space-time block code (STBC) encoder and a space-time block code (STBC) encoder for spreading a property point from N _SS spatial streams to N _STS space- transmit chains. < / RTI > The spatial mapper can use direct mapping, spatial expansion, beamforming, or the like.

The inverse Fourier transformer 140 transforms a sex store block output from the mapper 130 or the spatial mapper into an inverse discrete Fourier transform (IDFT) or an inverse fast Fourier transform (IFFT) Domain block, that is, a symbol. When the STBC encoder and the spatial mapper are used, the inverse Fourier transformer 140 may be provided for each transmission chain.

When SU-MIMO or MU-MIMO is used, the transmission signal processing unit may insert cyclic shift diversity (CSD) before or after inverse Fourier transform to prevent unintended beamforming. The CSD may be specified for each transport chain or for each space-time stream. Or CSD may be applied as part of a spatial mapper.

Also, when using MU-MIMO, some blocks before the space mapper may be provided for each user.

The GI inserter 150 inserts a GI in front of the symbol. The transmission signal processing unit 100 can smoothly window the edge of the symbol after inserting the GI. The RF transmitter 21 converts the symbol into an RF signal and transmits it via the antenna. In case of using SU-MIMO or MU-MIMO, the GI inserter 150 and the RF transmitter 21 can be provided for each transmission chain.

3 is a schematic block diagram illustrating a received signal processing unit in a wireless LAN.

3, the received signal processing unit 200 includes a GI eliminator 220, a Fourier transformer 230, a demapper 240, a deinterleaver 250, and a decoder 260.

The RF receiver 22 receives the RF signal through the antenna and converts it into a symbol, and the GI remover 220 removes the GI from the symbol. When using SU-MIMO or MU-MIMO, the RF receiver 22 and the GI remover 220 may be provided for each receive chain.

The Fourier transformer 230 transforms symbols, i.e., time domain blocks, into discrete Fourier transforms (DFTs) or fast Fourier transforms (FFTs) into frequency domain ghost points. Fourier transformer 230 may be provided for each receive chain.

When using SU-MIMO or MU-MIMO, it includes a spatial demapper that transforms the Fourier transformed reception chain into a spatiotemporal stream, and an STBC decoder that despreads the spots from the space-time stream to the spatial stream. can do.

The dem mapper 240 demaps the block of the sex store output from the Fourier transformer 230 or the STBC decoder into a bit stream. If the received signal is LDPC encoded, demapper 240 may perform further LDPC tone demapping before property demapping. The deinterleaver 250 deinterleaves the bits of the stream output from the demapper 240. Deinterleaving can be applied only when the received signal is BCC encoded.

When SU-MIMO or MU-MIMO is used, the reception signal processing unit 200 can use a plurality of demapper 240 and a plurality of deinterleavers 250 corresponding to the number of spatial streams. At this time, the received signal processing unit 200 may further include a stream deparser that combines the streams output from the plurality of deinterleavers 250.

The decoder 260 decodes the stream output from the deinterleaver 250 or the stream decoder, and may be, for example, an FEC decoder. The FEC decoder may include a BCC decoder or an LDPC decoder. The received signal processing unit 200 may further include a descrambler for descrambling the decoded data by the decoder 260. When a plurality of BCC decoders are used as the decoder 260, the received signal processing unit 200 may further include an encoder deparser for multiplexing the decoded data. When the LDPC decoder is used as the decoder 260, the received signal processing unit 200 may not use the encoder de-parser.

4 is a diagram showing an interframe space (IFS) relationship.

A data frame, a control frame, and a management frame may be exchanged between the wireless LAN devices.

A data frame is a frame used for transmission of data forwarded to an upper layer. The data frame is transmitted after performing a backoff after the DIFS (Distributed Coordination Function IFS) from when the medium becomes idle. The management frame is used for exchange of management information that is not forwarded to the upper layer, and is transmitted after backoff after IFS such as DIFS or PIFS (point coordination function IFS). The subtype frame of the management frame includes Beacon, Association request / response, probe request / response, and authentication request / response. A control frame is a frame used for controlling access to a medium. Subtype frames of the control frame include RTS, CTS, and ACK. The control frame is transmitted after backoff after DIFS elapses when it is not a response frame of another frame, and is transmitted without backoff after SIFS (short IFS) if it is a response frame of another frame. The type and subtype of the frame can be identified by the type field and the subtype field in the frame control field.

Meanwhile, the QoS (Quality of Service) STA can transmit an arbitration IFS (AIFS) for an access category (AC) to which a frame belongs, i.e., a frame after the backoff after the AIFS [AC] elapses. At this time, a frame in which AIFS [AC] can be used may be a control frame, not a data frame, a management frame, and a response frame.

FIG. 5 is an illustration of frame exchange of a Single User-Beamforming (SU-BF), and FIG. 6 is an illustration of frame exchange of a Multiple User-Beamforming (MU-BF)

Referring to FIGS. 5 and 6, for a downlink MIMO transmission, a transmitting device (to be referred to as an "AP" in the future) must know the channel status information of receiving devices (hereinafter, "STA"). The AP initiates a sounding protocol to obtain channel state information from at least one STA.

Referring to FIG. 5, the AP will transmit data to the STA. The AP initiates a sounding protocol by transmitting an NDP announcement (NDPA) frame before transmitting an NDP (null data packet) frame. The NDPA frame and the NDP frame are sounding frames. The NDP frame includes a training symbol for channel estimation.

The STA receiving the NDP frame transmits the channel information estimated based on the training symbol in a feedback frame.

)을 기초로 조향 행렬(steering matrix,

)을 계산한다. AP는 조향 행렬을 기초로 데이터 프레임을 전송하고, STA으로부터 ACK 프레임을 수신한다.The AP receives the beamforming feedback matrix (beamforming feedback matrix) obtained from the feedback frame,

Based on the steering matrix,

). The AP transmits the data frame based on the steering matrix and receives the ACK frame from the STA.

Referring to FIG. 6, the AP will transmit data to STA1 and STA2. Before data transmission, the AP transmits an NDPA frame and an NDP frame. The AP can use the NDPA frame to specify the responder to send a response after sending the NDP frame. The STA1 designated as the first responder receives the NDP frame, and then transmits the feedback frame. The AP explicitly transmits a Beamforming Report Poll frame to the remaining STA2, and receives a feedback frame from the STA2.

The AP computes the steering matrix based on the information of the feedback frames and transmits the beamformed data frame for multiple users. The AP receives an ACK frame from each STA.

)을 각도[

]의 형태로 압축한(compressed) 정보다. 여기서, 각도[

]는 약속된 방법으로 양자화된다. AP는 양자화된 각도를 수신하고, 수신 각도로부터 빔포밍 피드백 행렬(

)을 계산한다. AP는 빔포밍 피드백 행렬(

)을 이용하여 조향 행렬(

)를 계산한다. According to the IEEE 802.11ac standard, the feedback frame is a Compressed Beamforming (CB) frame. The CB frame includes feedback information that the STA (u) transmits on the subcarrier (k), and the feedback information includes a beamforming feedback matrix

) Angle [

It is compressed information in the form of []. Here, the angle [

] Are quantized in the promised way. The AP receives the quantized angles and generates a beamforming feedback matrix (< RTI ID = 0.0 >

). AP is a beamforming feedback matrix (

) And the steering matrix (

).

As described above, the CB frame quantizes and transmits the angle information. The amount of data increases considerably through quantization, and the size of the feedback information may exceed the size of the MAC data (MPDU) in some cases.

Next, an analog feedback method for reducing the overhead of the conventional CB frame will be described. Here, instead of modulating the feedback information by a modulation and coding scheme (MCS) and transmitting the analog feedback, the feedback information value that has not been converted into the binary data is transmitted. For example, when the feedback information is a complex number (a + jb), a conventional feedback method such as a CB frame converts a complex number to binary data, maps binary data to a property point, and then modulates the OFDM symbol. On the other hand, the analog feedback method modulates the complex numbers (a, b) into OFDM symbols. Therefore, analog feedback may have lower error correction performance than CB feedback, but it has the advantage of reducing overhead.

7 is an exemplary diagram illustrating a beamforming feedback method according to an embodiment of the present invention.

)에서 NDP 프레임(300)을 전송한다. NDP 프레임(300)은 고효율 무선랜(High Efficient WLAN, HEW)의 프레임일 수 있다. NDP 프레임(300)은 레가시(Legacy) 규격과의 호환을 위한 레가시 파트(L-part)(310), HEW 쇼트 트레이닝 필드(HEW-STF)(320) 그리고 롱 트레이닝 필드(LTF)(330)를 포함한다.Referring to FIG. 7, when a transmitting device (AP)

The NDP frame 300 is transmitted. The NDP frame 300 may be a frame of a high efficiency WLAN (HEW). The NDP frame 300 includes a L-part 310, a HEW short training field (HEW-STF) 320 and a long training field (LTF) 330 for compatibility with the Legacy standard .

The legacy part 310 may include a legacy short training field (L-STF), a legacy long training field (L-LTF), a legacy signal field (L-SIG), and a HEW signal field (HEW-SIG).

The HEW-STF 320 is positioned behind the leg part 310 and is used for automatic gain control (AGC).

The LTF 330 includes training symbols for channel estimation. LTF can be repeated. The number of repeated LTFs is related to the total number of space-time streams, which is determined by the number of antennas. For example, assuming that the number of antennas of the transmitting device (AP) is 2 (m = 2), the NDP frame 300 includes LTF1 and LTF2.

If the LTF sequence of any subcarrier is "1", the corresponding subcarrier signals of LTF1 and LTF2 transmitted by the first antenna of the transmitting device (AP) are 1, -1, and the corresponding subcarrier signals of LTF1 and LTF2 Is 1, 1. This can be expressed by the following equation (1). The first row (1, -1) in Equation 1 represents LTF1 and LTF2 transmitted by the first antenna and the second row (1, 1) in Equation 1 represents LTF1 and LTF2 transmitted by the second antenna .

)가 정방향 채널(

)을 통해 전송된 신호(

)를 수신한다. 정방향 채널(

)은 n x m 행렬로 표현되고, 2 x 2 MIMO 채널은 수학식 2와 같이 표현될 수 있다. 수신 신호(

)는 수학식 3과 같다.The receiving device (STA)

) Is a forward channel (

) ≪ / RTI >

). Forward channel (

) Is represented by an nxm matrix, and a 2 x 2 MIMO channel can be expressed by Equation (2). The received signal (

) ≪ / RTI >

)로부터 부반송파별로 정방향 채널(

)을 추정한다. 수신 디바이스(STA)는 추정 채널(

)로부터 빔포밍 피드백 행렬(

)을 계산한다. 빔포밍 피드백 행렬(

)을 계산하는 방법은 다양할 수 있다. 여기서는 수학식 4와 같이 추정 채널(

)을 특이치 분해(singular value decomposition, SVD)하여 빔포밍 피드백 행렬(

)을 계산하는 것으로 예시한다. 수학식 4에서,

와

는 유니터리 행렬(unitary matrix)이고,

는 대각 행렬(diagonal matrix)이다. 수신 디바이스(STA)는 추정 채널(

)의 특이치의 제곱을 계산하여 채널 이득을 구할 수 있다.The receiving device (STA)

) To the forward channel (< RTI ID = 0.0 >

). The receiving device (STA)

) To a beamforming feedback matrix (

). Beamforming feedback matrix (

) Can be varied. Here, as shown in Equation 4,

) Is singular value decomposition (SVD) to obtain a beamforming feedback matrix

). ≪ / RTI > In Equation (4)

Wow

Is a unitary matrix,

Is a diagonal matrix. The receiving device (STA)

) Can be calculated to obtain the channel gain.

)을 피드백 프레임(400)에 실어 송신 디바이스(AP)로 전송한다. 이때, 수신 디바이스(STA)는 부반송파별로 획득한 모든 빔포밍 피드백 행렬을 전송한다.The receiving device (STA) receives the beamforming feedback matrix (

) In the feedback frame 400 and transmits it to the transmitting device (AP). At this time, the receiving device (STA) transmits all the beamforming feedback matrices acquired for each subcarrier.

The feedback frame 400 includes a leg part 410, a HEW short training field (HEW-STF) 420, a long training field (LTF) 430, a feedback field (FB) 440, 450).

The legacy part 410 may include a short training field (L-STF), a long training field (L-LTF), a signal field (L-SIG), and a HEW signal field (HEW-SIG).

The LTF 430 includes training symbols for channel estimation, and the number of LTFs is determined according to the number of antennas. For example, if the number of antennas of the receiving device STA is 2 (n = 2), the feedback frame 400 includes LTF1 and LTF2.

)을 포함한다. 피드백 필드(440)의 수는 수신 디바이스(STA)의 안테나 수에 따라 결정된다. 예를 들어, 피드백 프레임(400)은 FB1과 FB2를 포함할 수 있다. 어느 부반송파(k)에 대한 빔포밍 피드백 행렬(

)을 피드백하는 경우, 수신 디바이스(STA)의 제1안테나에서 전송되는 FB1과 FB2의 해당 부반송파 신호는 v₁₁, v₁₂이고, 제2안테나에서 전송되는 FB1과 FB2의 해당 부반송파 신호는 v₂₁, v₂₂이다. 즉, 빔포밍 피드백 행렬(

)은 이진 데이터 변환 및 데이터 변조를 거치지 않고, 아날로그 정보 그대로 OFDM 변조된다. 이때, 수신 디바이스(STA)는 도 2를 참고로 설명한 바와 같이, 모든 부반송파에 대한 IFFT를 거쳐 OFMD 심볼을 생성한다. 수신 디바이스(STA)는 OFDM 심볼 앞에 GI를 추가할 수 있다. GI는 사이클릭 프리픽스(cyclic prefix, CP)로 형성될 수 있다.The feedback field 440 includes a beamforming feedback matrix

). The number of feedback fields 440 is determined according to the number of antennas of the receiving device (STA). For example, feedback frame 400 may include FB1 and FB2. The beamforming feedback matrix (k) for any subcarrier k

) For the case of feeding back, the sub-carrier signals FB1 and FB2 to be transmitted from a first antenna of the receiving device (STA) is v _11, v _12, and the sub-carrier signals FB1 and FB2 to be transmitted from the second antenna is v _21, v ₂₂ . That is, the beamforming feedback matrix (

) Is subjected to OFDM modulation as analog information without binary data conversion and data modulation. At this time, the receiving device STA generates an OFDM symbol through an IFFT for all subcarriers as described with reference to FIG. The receiving device (STA) may add GI in front of the OFDM symbol. The GI may be formed of a cyclic prefix (CP).

LTF1, LTF2, FB1, and FB2 transmitted from two sub-carriers of the receiving device STA are expressed by Equation (5). A first row of Equation _{5 (1, -1, v 11} , v 12) comprises a first antenna represents a LTF1, LTF2, FB1, FB2 to be transmitted, the second row of Equation 5 (1, 1, v ₂₁ , v ₂₂₎ represents a LTF1, LTF2, FB1, FB2 to transmit the second antenna.

The receiving device STA transmits the signal frame including the signal-to-noise ratio (SNR) information to the feedback frame 400. In the case of SU-BF, the receiving device (STA) can transmit the average SNR information of each subcarrier. In the case of MU-BF, the receiving device (STA) can transmit the difference between the average SNR and the SNR of each subcarrier and the average value. The SNR information may be inserted into the signal field or data field of the feedback frame 400.

)을 통해 전송된 신호(

)를 수신한다. 2 x 2 MIMO의 역방향 채널(

)은 수학식 6과 같고, 송신 디바이스(AP)가 수신한 신호(

)는 수학식 7과 같다.The transmitting device (AP) knows that the feedback frame (400)

) ≪ / RTI >

). 2 x 2 MIMO reverse channel (

Is expressed by Equation (6), and the signal received by the transmitting device (AP)

) ≪ / RTI >

)의 제1열과 제2열로부터 역방향 채널(

)을 구한다. 즉, 송신 디바이스(AP)는 피드백 프레임(400)의 LTF1과 LTF2로부터 채널 추정한다. 송신 디바이스(AP)는 역방향 채널(

)의 역행렬과 수신 신호(

)의 제3열과 제4열을 이용하여 빔포밍 피드백 행렬(

)을 구한다. 즉, 송신 디바이스(AP)는 피드백 프레임(400)의 FB1과 FB2에서 역방향 채널(

)의 영향을 제거하여 빔포밍 피드백 행렬(

)을 구한다. The transmitting device (AP)

) From the first and second columns of the reverse channel

). That is, the transmitting device (AP) performs channel estimation from LTF1 and LTF2 of the feedback frame (400). The transmitting device (AP) transmits the reverse channel

) And the received signal (

) Using the third and fourth columns of the beamforming feedback matrix (

). That is, the transmitting device (AP) transmits the feedback channel (FB) in the FB1 and FB2 of the feedback frame

) To remove the influence of the beamforming feedback matrix (

).

)을 피드백하는 방법을 유니터리 피드백 방법 또는 V 피드백 방법이라고 부를 수 있다. 이때, 빔포밍 피드백 행렬(

)은 양자화를 거치지 않은 값이므로 종래의 CB 프레임에 비해 오버헤드가 적다. As described above, when the receiving device (STA) receives the beamforming feedback matrix ("

) May be referred to as a unitary feedback method or a V feedback method. At this time, the beamforming feedback matrix (

) Is a value that has not been subjected to quantization, so that the overhead is smaller than that of the conventional CB frame.

8 is an exemplary diagram illustrating a beamforming feedback method according to another embodiment of the present invention.

)에서 NDP 프레임(300)을 전송한다. 송신 디바이스(AP)의 두 안테나가 송신하는 LTF1과 LTF2는 수학식 1과 같다고 가정한다.Referring to FIG. 8, when a transmitting device (AP) receives a forward channel

The NDP frame 300 is transmitted. It is assumed that LTF1 and LTF2 transmitted by the two antennas of the transmitting device (AP) are as shown in Equation (1).

)가 정방향 채널(

)을 통해 전송된 신호(

)를 수신한다. The receiving device (STA)

) Is a forward channel (

) ≪ / RTI >

).

)로부터 부반송파별 정방향 채널(

)을 추정한다. 추정 채널(

)은 수신측의 잡음(n)을 포함한다. 예를 들면, 정방향 채널(

)은 수학식 2와 같고, 수신 신호(

)는 수학식 3과 같다.The receiving device (STA)

) To the forward channel for each subcarrier (

). Estimated channel (

(N) on the receiving side. For example, a forward channel (

(2), and the received signal

) ≪ / RTI >

)을 피드백 프레임(400)에 실어 송신 디바이스(AP)로 전송한다. 수신 디바이스(STA)는 추정 채널(

)을 정규화(normalized)하여 전송할 수 있다.The receiving device (STA)

) In the feedback frame 400 and transmits it to the transmitting device (AP). The receiving device (STA)

) Can be normalized and transmitted.

)을 포함한다. 예를 들어, 수신 디바이스(STA)의 안테나 수가 2(n=2)인 경우, 피드백 프레임(400)은 FB1과 FB2를 포함한다. 어느 부반송파(k)에 대한 채널 행렬(

)을 피드백하는 경우, 수신 디바이스(STA)의 제1안테나에서 전송되는 FB1과 FB2의 해당 부반송파 신호는 h₁₁, h₁₂이고, 제2안테나에서 전송되는 FB1과 FB2의 해당 부반송파 신호는 h₂₁, h₂₂이다. 즉, 추정 채널(

)은 이진 데이터 변환 및 데이터 변조를 거치지 않고, 아날로그 정보 그대로 OFDM 변조된다.The feedback field 440 of the feedback frame 400 includes the estimated channel

). For example, if the number of antennas of the receiving device (STA) is 2 (n = 2), the feedback frame 400 includes FB1 and FB2. The channel matrix for any subcarrier (k)

) The case of feedback, receiving the sub-carrier signals FB1 and FB2 to be transmitted from the first antenna device (STA) is h _11, the sub-carrier signals FB1 and FB2 to be transmitted from and h _12, the second antenna is h _21, h ₂₂ . That is,

) Is subjected to OFDM modulation as analog information without binary data conversion and data modulation.

LTF1, LTF2, FB1, and FB2 transmitted from two sub-carriers of the receiving device STA are expressed by Equation (8). A first row of Equation _{8 (1, -1, h 11} , h 12) has a first antenna represents a LTF1, LTF2, FB1, FB2 to be transmitted, the second row of Equation 5 (1, 1, ₁₁ h , h ₁₂₎ represents a LTF1, LTF2, FB1, FB2 to transmit the second antenna.

The receiving device STA transmits the signal frame including the signal-to-noise ratio (SNR) information to the feedback frame 400. In the case of SU-BF, the receiving device (STA) can transmit the average SNR information of each subcarrier. In the case of MU-BF, the receiving device (STA) can transmit the difference between the average SNR and the SNR of each subcarrier and the average value. The SNR information may be inserted into the signal field or data field of the feedback frame 400.

)을 통해 전송된 신호(

)를 수신한다. 2 x 2 MIMO의 역방향 채널(

)은 수학식 6과 같고, 송신 디바이스(AP)가 수신한 신호(

)는 수학식 9과 같다.The transmitting device (AP) knows that the feedback frame (400)

) ≪ / RTI >

). 2 x 2 MIMO reverse channel (

Is expressed by Equation (6), and the signal received by the transmitting device (AP)

) ≪ / RTI >

)의 제1열과 제2열로부터 역방향 채널(

)을 구한다. 즉, 송신 디바이스(AP)는 피드백 프레임(400)의 LTF1과 LTF2로부터 역방향 채널을 추정한다. 송신 디바이스(AP)는 역방향 채널(

)의 역행렬과 수신 신호(

)의 제3열과 제4열을 이용하여 정방향 채널(

)을 추출한다. 즉, 송신 디바이스(AP)는 피드백 프레임(400)의 FB1과 FB2로부터 역방향 채널(

)의 영향을 제거하여 정방향 채널(

)을 구한다. 송신 디바이스(AP)는 정방향 채널(

)을 특이치 분해하여 빔포밍 피드백 행렬(

)을 계산한다.The transmitting device (AP)

) From the first and second columns of the reverse channel

). That is, the transmitting device (AP) estimates the reverse channel from LTF1 and LTF2 of the feedback frame (400). The transmitting device (AP) transmits the reverse channel

) And the received signal (

) And the third and fourth columns of the forward channel < RTI ID = 0.0 >

. That is, the transmitting device (AP) receives the feedback signal from the FB1 and the FB2 of the feedback frame (400)

) To remove the influence of the forward channel (

). The transmitting device (AP) transmits the forward channel

) Is singly decomposed into a beamforming feedback matrix (

).

As described above, a method of feeding back the estimated channel by the receiving device (STA) may be referred to as a channel feedback method or an H feedback method. At this time, since the estimated channel is a value not subjected to quantization, the overhead is smaller than that of the conventional CB frame.

FIG. 9 is a flowchart of a method of feeding back a beamforming feedback matrix according to an embodiment of the present invention, and FIG. 10 is a flowchart of a method of feeding back an estimated channel matrix according to another embodiment of the present invention.

Referring to FIG. 9, a transmitting device (AP) transmits an NDPA frame (S110). The NDPA frame may include an indication of the feedback mode and may indicate, for example, V feedback.

The transmitting device (AP) transmits an NDP frame including a training symbol for channel estimation (S120).

The receiving device (STA) estimates the forward channel using the training symbol of the NDP frame (S130).

)로부터 빔포밍 피드백 행렬(

)을 계산한다(S140). 수신 디바이스(STA)는 특이치 분해(SVD) 방법을 이용하여 빔포밍 피드백 행렬(

)을 계산할 수 있다.The receiving device (STA)

) To a beamforming feedback matrix (

(S140). The receiving device (STA) uses a singular value decomposition (SVD) method to generate a beamforming feedback matrix

) Can be calculated.

)을 포함하는 피드백 프레임을 전송한다(S150). 빔포밍 피드백 행렬(

)은 피드백 프레임(400)의 피드백 필드(440)에 설정된다. 피드백 필드의 수는 안테나의 수에 따라 결정된다. 빔포밍 피드백 행렬(

)은 트레이닝 심볼들과 함께 복수의 안테나에서 전송된다. 이때, 빔포밍 피드백 행렬(

)에 수신측 잡음(n)이 더해진 값(

)이 피드백 프레임에 삽입된다.The receiving device (STA) receives the beamforming feedback matrix (

(S150). ≪ / RTI > Beamforming feedback matrix (

Is set in the feedback field 440 of the feedback frame 400. [ The number of feedback fields is determined by the number of antennas. Beamforming feedback matrix (

) Is transmitted on a plurality of antennas with training symbols. At this time, the beamforming feedback matrix (

(N) is added to the reception side noise

) Is inserted in the feedback frame.

The transmitting device (AP) estimates the reverse channel using the training symbol of the feedback frame (S160).

]를 채널 등화하여 빔포밍 피드백 행렬(

)을 추출한다. 추출된 빔포밍 피드백 행렬은 수신 디바이스(STA)측 잡음(n)과 송신 디바이스(AP)측 잡음(w)을 포함한다.The transmitting device (AP) extracts the beamforming feedback matrix by removing the reverse channel from the signal related to the feedback field of the feedback frame (S170). In the feedback field of the feedback frame,

] To equalize the beamforming feedback matrix (

. The extracted beamforming feedback matrix includes a receiving device (STA) side noise (n) and a transmitting device (AP) side noise (w).

The transmitting device AP transmits the beamformed data frame with the extracted beamforming feedback matrix (S180).

Referring to FIG. 10, a transmitting device (AP) transmits an NDPA frame (S210). The NDPA frame may include an indicator indicating the feedback mode and may indicate, for example, H feedback.

The transmitting device (AP) transmits an NDP frame including a training symbol for channel estimation (S220).

)은 실제 채널(

)에 수신측 잡음(n)이 더해진다.The receiving device (STA) estimates the forward channel using the training symbol of the NDP frame (S230). Estimated channel (

) Is the actual channel

(N) is added to the reception-side noise n.

)을 포함하는 피드백 프레임을 전송한다(S240). 추정 채널(

)은 피드백 프레임(400)의 피드백 필드(440)에 설정된다. 피드백 필드의 수는 안테나의 수에 따라 결정된다. 추정 채널(

)은 트레이닝 심볼들과 함께 복수의 안테나에서 전송된다. The receiving device (STA) transmits the estimated forward channel (

(S240). ≪ / RTI > Estimated channel (

Is set in the feedback field 440 of the feedback frame 400. [ The number of feedback fields is determined by the number of antennas. Estimated channel (

) Is transmitted on a plurality of antennas with training symbols.

The transmitting device (AP) estimates the reverse channel using the training symbol of the feedback frame (S250).

]를 채널 등화하여 정방향 채널(

)을 추출한다. 추출된 정방향 채널은 수신 디바이스(STA)측 잡음(n)과 송신 디바이스(AP)측 잡음(w)을 포함한다.The transmitting device AP extracts the forward channel matrix by removing the reverse channel from the signal related to the feedback field of the feedback frame (S260). In the feedback field of the feedback frame,

] Is channelized to a forward channel (

. The extracted forward channel includes a noise (n) on the receiving device (STA) and a noise (w) on the transmitting device (AP).

)을 계산한다(S270).The transmitting device (AP) performs singular value decomposition on the extracted forward channel matrix and outputs the beamforming feedback matrix

(S270).

The transmitting device AP transmits the beamformed data frame with the beamforming feedback matrix (S280).

11 is a diagram showing an NDPA MAC frame in a wireless LAN.

11, the NDPA frame 500 includes a frame control field, a duration field, a receiver address (RA) field, a transmitter address (TA) field, a sounding conversation token a sounding dialog token field, an information (STA info) field of wireless LAN devices, and a frame check sequence (FCS) field.

The feedback mode indicator indicating the feedback mode may be set to at least one bit specified in the NDPA frame 500. If the wireless LAN device supports, for example, three feedback modes, the feedback mode indicator may be set as shown in Table 1.

Feedback mode value meaning 0 The channel is quantized with angle information to provide feedback One The beamforming feedback matrix is fed back (V feedback) 2 The estimated channel matrix is fed back (H feedback)

The receiving device feeds back the channel information according to the feedback mode indicated in the NDPA frame.

The method of feedbacking the beamforming feedback matrix (V feedback) and the method of feedbacking the estimated channel matrix (H feedback) are analog feedback. Analog feedback can reduce feedback overhead and transmit feedback information quickly. Therefore, when the channel change is fast or when the amount of data to be beamformed is small, the transmitting device can select the analog feedback mode to reduce the feedback information reception time. On the other hand, when it is more important to correctly receive the feedback information, the transmitting device can select the feedback mode in which the channel information is modulated and transmitted.

Further, when the method of feeding back the beamforming feedback matrix (V feedback) and the method of feeding back the estimated channel matrix (H feedback) are compared, the V feedback is a singular value decomposition (SVD ), And the H feedback performs singular value decomposition (SVD) on the signal to which noise on the receiving device (STA) side and the transmitting device (AP) side is added. Thus, in low SNR environments, H feedbacks may exhibit fewer errors, and at higher SNRs, V feedback may indicate fewer errors. Thus, the transmitting device can select V-feedback or H-feedback based on the channel environment.

The beamforming feedback method of the present invention described with reference to FIGS. 1 to 11 is performed in a wireless LAN device including a processor, a memory, and a transceiver. The wireless LAN device may store instructions for performing the beamforming feedback method of the present invention or may be a memory for loading and temporarily storing instructions from a storage device and executing commands stored or loaded in the memory, And a transceiver for transmitting frames generated in the processor or receiving frames transmitted over the wireless communication network. 1. The processor may include the baseband processor 10 of FIG. 1 and the memory may include the memory 40 of FIG. 1 and the transceiver may include the RF transceiver 20 and the antenna unit 30 of FIG. . ≪ / RTI >

The embodiments of the present invention described above are not implemented only by the apparatus and method, but may be implemented through a program for realizing the function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded.

While various embodiments of the present invention have been described above, it is to be understood that these various embodiments are not necessarily implemented alone, and that more than two embodiments may be combined. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (20)

A beamforming feedback method of a device in a wireless local area network (WLAN)
Receiving a first frame from a transmitting device that is scheduled to transmit beamforming data,
Estimating a forward channel based on the first frame,
Calculating a beamforming feedback matrix from the forward channel, and
Transmitting a second frame including the beamforming feedback matrix to the transmitting device
/ RTI > The method of claim 1,
The step of transmitting the second frame
Inserting the beamforming feedback matrix into a feedback field of the second frame,
Wherein the feedback field is located between a training field and a data field of the second frame. 3. The method of claim 2,
The step of transmitting the second frame
And transmitting information of the training field and the feedback field on a subcarrier of each antenna. The method of claim 1,
To-noise ratio information of a subcarrier into a signal field or a data field of the second frame
≪ / RTI > The method of claim 1,
Before receiving the first frame, receiving a notification frame informing of the first frame transmission from the transmitting device
Further comprising:
Wherein the notification frame includes an indicator requesting transmission of a beamforming feedback matrix. The method of claim 1,
The beamforming feedback matrix is a unitary matrix,
The step of calculating the beamforming feedback matrix
And calculating the unitary matrix by singular value decomposition of the forward channel. A beamforming feedback method of a device in a wireless local area network (WLAN)
Transmitting a first frame to a receiving device that is scheduled to receive beamforming data,
Receiving a second frame comprising analog feedback information from the receiving device,
Estimating an uplink channel based on the second frame, and
Equalizing the reverse channel and extracting the analog feedback information in the second frame
/ RTI > 8. The method of claim 7,
Wherein the analog feedback information is included in a feedback field of the second frame,
Wherein the feedback field is located between a training field and a data field of the second frame. 9. The method of claim 8,
The step of extracting the analog feedback information
And calculating the analog feedback information by equalizing the reverse channel in a signal related to the feedback field of the received signal. 8. The method of claim 7,
Wherein the analog feedback information is a beamforming feedback matrix. 11. The method of claim 10,
Beamforming a data frame using the extracted beamforming feedback matrix
≪ / RTI > 8. The method of claim 7,
Wherein the analog feedback information is a forward channel matrix estimated by the receiving device. The method of claim 12,
Calculating a beamforming feedback matrix by singular value decomposition of the extracted forward channel matrix, and
Beamforming a data frame using the beamforming feedback matrix
≪ / RTI > 8. The method of claim 7,
Further comprising: before the first frame transmission, transmitting a notification frame informing the receiving device of the first frame transmission,
Wherein the notification frame includes a feedback mode indicator,
And the second frame includes analog feedback information corresponding to the feedback mode indicator. A beamforming feedback method of a device in a wireless local area network (WLAN)
Transmitting a Null Data Packet Announcement (NDPA) frame indicating a feedback mode to a receiving device,
Transmitting a Null Data Packet (NDS) frame to the receiving device, and
Receiving a feedback frame including feedback information generated according to the feedback mode
/ RTI > 16. The method of claim 15,
The feedback mode
A first mode for quantizing and feeding back the channel to the angle information, a second mode for feeding back the beamforming feedback matrix, and a third mode for feeding back the estimated channel matrix. 17. The method of claim 16,
If the NDPA frame indicates the second mode, the feedback frame includes a beamforming feedback matrix in a feedback field,
Wherein the feedback field is located between a training field and a data field of the feedback frame. The method of claim 17,
Estimating an uplink channel based on the feedback frame, and
Equalizing the reverse channel to extract the beamforming feedback matrix in the feedback frame
≪ / RTI > 17. The method of claim 16,
If the NDPA frame indicates the third mode, the feedback frame includes a forward channel matrix estimated in the receiving device in a feedback field,
Wherein the feedback field is located between a training field and a data field of the feedback frame. 20. The method of claim 19,
Estimating an uplink channel based on the feedback frame,
Equalizing the reverse channel to extract the forward channel matrix in the feedback frame, and
Calculating a beamforming feedback matrix by singular value decomposition of the extracted forward channel matrix;
≪ / RTI >

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