WO2015156495A1 - 사운딩 절차 기반의 프레임 전송 방법 및 장치 - Google Patents
사운딩 절차 기반의 프레임 전송 방법 및 장치 Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
- H04L5/005—Allocation of pilot signals, i.e. of signals known to the receiver of common pilots, i.e. pilots destined for multiple users or terminals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04W74/08—Non-scheduled access, e.g. ALOHA
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0417—Feedback systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0452—Multi-user MIMO systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
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- H04W74/002—Transmission of channel access control information
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0003—Two-dimensional division
- H04L5/0005—Time-frequency
- H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
- H04L5/001—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT the frequencies being arranged in component carriers
Definitions
- the present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting a frame based on a sounding procedure.
- the WLAN system may support a downlink multi-user multiple input multiple output (MU-MIMO) transmission method for higher throughput.
- the AP may simultaneously transmit data frames to at least one or more STAs paired with MIMO through downlink.
- the number of paired STAs may be up to four, and when the maximum number of spatial streams is eight, up to four spatial streams may be allocated to each STA.
- an AP may simultaneously transmit data to an STA group including at least one or more STAs among a plurality of STAs associated with the AP.
- an STA group including at least one or more STAs among a plurality of STAs associated with the AP.
- the STA that wants to transmit data is MU-MIMO.
- the PPDU may be transmitted to a plurality of STAs through downlink using the MIMO transmission technique.
- MU-MIMO data transmitted to each STA may be transmitted through different spatial streams.
- An object of the present invention is to provide a frame receiving method based on the sounding procedure.
- Another object of the present invention is to provide an apparatus for performing a frame receiving method based on a sounding procedure.
- a frame transmission method based on a sounding procedure in a wireless LAN provides an access point (AP) to each of a plurality of STAs (null data packet announcement). Transmitting a frame, wherein the NDPA frame notifies transmission of a null data packet (NDP), the AP transmitting the NDP to each of the plurality of STAs, and the AP is overlapped by each of the plurality of STAs.
- AP access point
- NDP null data packet
- Each of the plurality of feedback frames may include a plurality of channel state information determined based on the NDP, and the plurality of downlink frames. Each may be transmitted based on the plurality of channel state information after each reception of each of the plurality of the feedback frame within a predetermined time.
- the AP is implemented to transmit or receive a radio signal A radio frequency (RF) unit and a processor operatively connected to the RF unit, wherein the processor transmits a null data packet announcement (NDPA) frame to each of a plurality of STAs, wherein the NDPA frame Notifies transmission of a null data packet (NDP), transmits the NDP to each of the plurality of STAs, and transmits each of the plurality of transmission resources allocated to each of the plurality of STAs on a time resource superimposed by each of the plurality of STAs.
- RF radio frequency
- Data transmission efficiency may be increased by transmitting a frame based on channel state information obtained based on a sounding procedure.
- WLAN wireless local area network
- FIG. 2 is a conceptual diagram illustrating an interval between frames.
- FIG. 4 is a conceptual diagram illustrating a frame transmission method based on a sounding procedure according to an embodiment of the present invention.
- FIG. 5 is a conceptual diagram illustrating a format of an NDPA PPDU according to an embodiment of the present invention.
- FIG. 6 is a conceptual diagram illustrating an NDP according to an embodiment of the present invention.
- FIG. 7 is a conceptual diagram illustrating a feedback PPDU according to an embodiment of the present invention.
- FIG. 8 is a conceptual diagram illustrating a frame transmission method based on a sounding procedure according to an embodiment of the present invention.
- FIG. 10 is a conceptual diagram illustrating a frame transmission method based on a sounding procedure according to an embodiment of the present invention.
- FIG. 11 is a conceptual diagram illustrating a format of an NDPA PPDU according to an embodiment of the present invention.
- FIG. 12 is a conceptual diagram illustrating an NDP according to an embodiment of the present invention.
- FIG. 13 is a conceptual diagram illustrating a PPDU format for a sounding procedure according to an embodiment of the present invention.
- FIG. 14 is a conceptual diagram illustrating a PPDU format for transmitting an ACK frame according to an embodiment of the present invention.
- 15 is a block diagram illustrating a wireless device to which an embodiment of the present invention can be applied.
- WLAN wireless local area network
- BSS infrastructure basic service set
- IEEE Institute of Electrical and Electronic Engineers
- the WLAN system may include one or more infrastructure BSSs 100 and 105 (hereinafter, BSS).
- BSSs 100 and 105 are a set of APs and STAs such as an access point 125 and a STA1 (station 100-1) capable of successfully synchronizing and communicating with each other, and do not indicate a specific area.
- the BSS 105 may include one or more joinable STAs 105-1 and 105-2 to one AP 130.
- the distributed system 110 may connect several BSSs 100 and 105 to implement an extended service set (ESS) 140 which is an extended service set.
- ESS 140 may be used as a term indicating one network in which one or several APs 125 and 230 are connected through the distributed system 110.
- APs included in one ESS 140 may have the same service set identification (SSID).
- the portal 120 may serve as a bridge for connecting the WLAN network (IEEE 802.11) with another network (for example, 802.X).
- a network between the APs 125 and 130 and a network between the APs 125 and 130 and the STAs 100-1, 105-1 and 105-2 may be implemented. However, it may be possible to perform communication by setting up a network even between STAs without the APs 125 and 130.
- a network that performs communication by establishing a network even between STAs without APs 125 and 130 is defined as an ad-hoc network or an independent basic service set (BSS).
- FIG. 1 is a conceptual diagram illustrating an IBSS.
- the IBSS is a BSS operating in an ad-hoc mode. Since IBSS does not contain an AP, there is no centralized management entity. That is, in the IBSS, the STAs 150-1, 150-2, 150-3, 155-4, and 155-5 are managed in a distributed manner. In the IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may be mobile STAs, and access to a distributed system is not allowed, thus making a self-contained network. network).
- a STA is any functional medium that includes medium access control (MAC) conforming to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface to a wireless medium. May be used to mean both an AP and a non-AP STA (Non-AP Station).
- MAC medium access control
- IEEE Institute of Electrical and Electronics Engineers
- the STA may include a mobile terminal, a wireless device, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit ( It may also be called various names such as a mobile subscriber unit or simply a user.
- WTRU wireless transmit / receive unit
- UE user equipment
- MS mobile station
- UE mobile subscriber unit
- It may also be called various names such as a mobile subscriber unit or simply a user.
- FIG. 2 is a conceptual diagram illustrating an interval between frames.
- a time interval between two frames transmitted on a medium may be referred to as interframe space (IFS).
- IFS interframe space
- Priority of the STA occupying the wireless medium may be determined based on different lengths of IFS.
- Frames transmitted on the medium may be transmitted based on different lengths of IFS. For example, different IFSs can be used for the transmission of frames on the medium.
- PCF IFS PIFS
- PCF frames e.g., channel switch announcement frame, traffic indication map (TIM) frame, etc.
- PCF point coordination function
- DIFS used for frame transmission of an STA performing DCF based channel access.
- SIFS (16 ⁇ s) aRxRFDelay (0.5) + aRxPLCPDelay (12.5) + aMACProcessingDelay (1 or ⁇ 2) + aRxTxTurnaroundTime ( ⁇ 2)
- SIFS may be a value in consideration of a radio frequency (RF) stage delay, a physical layer convergence protocol (PLCP) stage delay, a medium access control (MAC) processing delay, and a transition time from Rx to Tx.
- RF radio frequency
- PLCP physical layer convergence protocol
- MAC medium access control
- the SIFS may be from the time of receiving the last symbol of the received frame from the medium (or air interface) to the time of sending the first symbol of the transmission frame to the medium (or air interface).
- PIFS (25 ⁇ s) aSIFSTime + aSlotTime
- aSlotTime aCCATime ( ⁇ 4) + aRxTxTurnaroundTime ( ⁇ 2) + aAirPropagationTime ( ⁇ 1) + aMACProcessingDelay ( ⁇ 2)
- aAirProgationTime may be twice the propagation time (or propagation delay) for signal transmission on the maximum distance between the slot-synchronized STAs of the longest distance in the communication range.
- aAirProgationTime may be a value of 1 ⁇ s or less.
- the radio wave may be propagated at 300 m / ⁇ s.
- DIFS distributed (coordination function) interframe space
- 34 ⁇ s aSIFSTime + 2 ⁇ aSlotTime
- values of SIFS, PIFS, and DIFS may vary depending on the capability of the STA and / or the wireless communication environment.
- SIFS may have a value of up to 16 ⁇ s
- PIFS may have a value of at least 16 ⁇ s and up to 25 ⁇ s, depending on the capability of the STA and / or the wireless communication environment.
- An access point (AP) operating in a wireless local area network (WLAN) system may transmit data through the same time resource to each of a plurality of stations (STAs). If the transmission from the AP to the STA is called downlink transmission, the transmission of the AP may be expressed in terms of DL MU transmission (downlink multi-user transmission).
- the AP could perform DL MU transmission based on MU MIMO, and this transmission may be expressed by the term DL MU MIMO transmission.
- the AP may perform DL MU transmission based on OFDMA, and such transmission may be expressed by the term DL MU OFDMA transmission.
- the AP may transmit a downlink frame to each of the plurality of STAs through each of the plurality of frequency resources on the overlapped time resources.
- the PPDU may be a data unit including a PPDU header and a physical layer service data unit (PDSU) (or MAC protocol data unit (MPDU)).
- the PPDU header may include a PHY header and a PHY preamble, and the PDSU (or MPDU) may include or indicate a frame.
- transmission from the STA to the AP may be referred to as uplink transmission, and a plurality of STAs may transmit the data to the AP on the same time resource in terms of UL MU transmission (uplink multi-user transmission).
- the UL MU transmission may be supported in the WLAN system according to an exemplary embodiment of the present invention.
- Each of the PPDUs, frames, and data transmitted through uplink transmission may be expressed in terms of uplink PPDU, uplink frame, and uplink data.
- Uplink transmission by each of the plurality of STAs may be performed in a frequency domain or a spatial domain.
- different frequency resources may be allocated as uplink transmission resources for each of the plurality of STAs based on orthogonal frequency division multiplexing (OFDMA).
- OFDMA orthogonal frequency division multiplexing
- Each of the plurality of STAs may transmit an uplink frame to the AP through different allocated frequency resources.
- the transmission method through these different frequency resources may be represented by the term UL MU OFDMA transmission method.
- each of the plurality of STAs When uplink transmission by each of the plurality of STAs is performed on the spatial domain, different spatial streams are allocated to each of the plurality of STAs, so that each of the plurality of STAs may transmit an uplink frame to the AP through different spatial streams.
- the transmission method through these different spatial streams may be represented by the term UL MU MIMO transmission method.
- the X axis represents an experiment time from 2000 ms to 5000 ms
- the Y axis is SINR over time. Referring to the graph, it can be seen that the magnitude of change in the SINR value is large for each transmission for each frame. In this case, it may be difficult to determine a parameter (modulation and coding scheme) according to a channel state for transmission of the current frame based on the SINR information of the previous frame fed back.
- the first may be no feedback for SINR.
- the STA performs a cyclic redundancy check (CRC) starting from the modulation and coding scheme (MCS) level (or index) 0 and increases the size of the MCS level (or index) by 1 after 10 successful transmissions.
- CRC cyclic redundancy check
- MCS modulation and coding scheme
- the MCS level can be decreased by one.
- the STA subtracts or adds the SINR margin (eg, 0.5 dB, 2 dB) from the current SINR according to the CRC check information of the previous frame and / or whether the ACK frame is received, thereby adding feedback information (or channel state information). ) May determine channel variable information (eg, MCS).
- SINR margin eg, 0.5 dB, 2 dB
- the STA may generate feedback information based on the NDPA frame, NDP received from the AP within a threshold time (eg, SIFS time) based on the current frame.
- feedback information may be generated through a frame obtained on a TXOP set based on an RTS frame and a CTS frame transmission and reception procedure.
- Table 1 below shows downlink throughput and uplink throughput when the feedback information is obtained on the TXOP of the previous frame, when the feedback information is obtained on the TXOP of the current frame, when the feedback information is not received. throughput).
- the downlink throughput and the uplink compared with the case of No feedback and Feedback (previous) It may have a relatively high performance in terms of link throughput.
- a procedure of acquiring feedback information based on a sounding procedure using an NDPA frame is defined.
- the transmission timing of the frame based on the obtained feedback information is not defined.
- the STA in order to transmit a frame based on feedback information, the STA performs channel access on a contention-based basis. In this case, the interval between the timing of acquiring the feedback information of the STA and the transmission timing of the frame based on the feedback information of the STA may be increased. Increasing the interval between these timings may cause performance degradation, as shown in Table 1 above.
- the DL MU transmission according to the embodiment of the present invention, the UL MU transmission based on the feedback information is received, and for the transmission of the downlink frame according to the feedback information, DL MU transmission based on the DL frame is received, UL MU A grouping procedure for a plurality of STAs for transmitting a transmission-based uplink frame may be needed.
- the gain based on the feedback information may not be large.
- the STA determines the channel variable information (MCS, the number of streams, the beamforming vector, etc.) based on the feedback information included in the feedback frame transmitted in the adjacent time, and determines the frame.
- MCS channel variable information
- the AP acquires feedback information from the STA and based on the obtained feedback information, the downlink frame (eg, a downlink data frame, a downlink management frame) may be transmitted. Discuss how to transmit.
- the AP is an STA. It may be interpreted.
- the STA acquires feedback information and transmits an uplink frame based on the obtained feedback information, transmission / reception of a data unit (eg, PPDU or frame) based on a sounding procedure according to an embodiment of the present invention. Procedures may apply.
- FIG. 4 is a conceptual diagram illustrating a frame transmission method based on a sounding procedure according to an embodiment of the present invention.
- a method of transmitting a frame based on a sounding procedure for one STA is disclosed.
- the sounding procedure may be a procedure for obtaining channel state information.
- the present invention discloses a method in which an AP performs a sounding procedure with an STA and transmits a downlink frame to the STA based on SU-MIMO (or OFDMA) based on feedback information obtained based on the sounding procedure.
- SU-MIMO or OFDMA
- the AP may transmit a null data packet anouncement (NDPA) frame 400 to the STA for the sounding procedure, and may transmit the NDP 410 after a predetermined time (eg, short interframe space (SIFS)).
- NDPA null data packet anouncement
- SIFS short interframe space
- the NDPA frame 400 may inform the STA of the start of the sounding procedure and transmission of the NDP 410.
- the NDPA frame 400 may include a STA information field.
- the STA information field may receive an NDP 410 to be transmitted after the NDPA frame 400 and indicate an STA to transmit a feedback frame.
- the STA indicated based on the STA information field may estimate a channel based on the NDP 410 and transmit a feedback frame 420 including the channel state information to the AP. That is, the STA may determine whether to transmit the feedback frame 420 to the AP by participating in channel sounding based on the STA information field included in the received NDPA frame 400.
- the NDP 410 may have a format in which a data field is omitted from a general PPDU and includes only a PPDU header.
- the NDP 410 may be precoded by the AP based on a specific precoding matrix.
- the STA that receives the NDP 410 may estimate a channel based on a training field (eg, HE-LTF) of the NDP 410 and obtain channel state information. Since the NDP 410 has no data field, the length information indicating the length of the PSDU included in the data field of the NDP 410 or the length of the Aggregate-MAC protocol data unit (A-MPDU) included in the PSDU may be set to 0. have.
- a training field eg, HE-LTF
- Each of the NDPA frame 400 and the NDP 410 may be transmitted through the entire bandwidth for the transmission of the NDPA frame 400 and the NDP 410.
- the format of such a PPDU may be expressed in terms of a non-duplicate format.
- each of the NDPA frame 400 and the NDP 410 may be transmitted through a plurality of channels based on a duplicate PPDU format.
- the duplicate PPDU format replicates the PPDU format transmitted over adjacent channels (or primary channels) (20 MHz), over bandwidths greater than 20 MHz (eg, 40 MHz, 80 MHz, 160 MHz, 80 MHz + 80 MHz, etc.). Can be sent.
- the duplicate format 450 is used, the same data may be transmitted through each of a plurality of channels (a replication target channel and a replication channel).
- an NDPA PPDU (or NDP) based on a duplicate format that transmits duplicated information through each of a plurality of channels may be used.
- the AP may transmit the NDPA frame 400 and the NDP 410 to one STA through at least one stream.
- the NDPA frame 400 may indicate at least one STA to transmit the feedback frame.
- the LTF is transmitted through at least one spatiotemporal stream through the NDP 410, and the STA may transmit a feedback frame including channel state information measured based on the indicated spatiotemporal stream and the LTF of the indicated frequency domain to the AP.
- the NDPA frame 400 and the NDP 410 may be transmitted based on the DL MU transmission method.
- the NDPA frame 400 and the NDP 410 are transmitted to a plurality of STAs through different space-time streams based on DL MU MIMO transmission, or different frequency resources (or subbands and channels) based on DL MU OFDMA. It may be transmitted to a plurality of STAs.
- the NDPA frame 400 and the NDP 410 transmitted through different space-time streams or different frequency resources may include information that is not the same.
- the AP may transmit each of the plurality of NDPA frames to each of the plurality of STAs and each of the plurality of NDPs to each of the plurality of STAs.
- an NDPA frame transmitted through a specific space-time stream or a specific frequency resource may indicate only a specific STA to transmit a feedback frame.
- the NDPA frame and the NDP are transmitted to at least one STA through at least one stream based on the non-duplicate PPDU format or the duplicate PPDU format.
- the STA may perform channel measurement based on the NDP 410 and transmit the obtained channel state information to the AP through the feedback frame 420.
- the channel bandwidth used for the transmission of the feedback frame 420 may be set to be smaller than or equal to the channel bandwidth used for the transmission of the NDPA frame 400.
- the feedback frame 420 may include channel state information (or stream state information) for each of the indicated space time streams (or spatial streams).
- the feedback frame 420 may include a high throughput (HT) control field and a channel information control field (for example, a very high throughput MIMO control field or a HE MU control). Field).
- the HT control field may include information on Nsts (number of space-time streams), MCS, bandwidth (BW), and SNR, and the channel information control field may be reserved.
- the STA may transmit the feedback frame 420 to the AP after a predetermined time (eg, SIFS) after receiving the NDP 410.
- the AP may receive the feedback frame 420 and transmit the downlink frame 430 on the SU MIMO (or OFDMA / MU-MIMO) basis to the STA after a predetermined time (eg, SIFS).
- the AP may transmit the downlink frame 430 generated based on the channel variable information determined in consideration of the channel state information included in the feedback frame 420.
- the STA may transmit an ACK or a block ACK for the received downlink frame 430 to the AP.
- the fed back channel state parameters eg, Nsts, MCS, BW, SNR, Nc, Nr, Ng, SNR information per stream, information on a beamforming feedback matrix per subcarrier, and frequency resource (eg, SNR information per subband) in OFDMA-based transmission are relatively accurate, thereby increasing data transmission efficiency.
- FIG. 5 is a conceptual diagram illustrating a format of an NDPA PPDU according to an embodiment of the present invention.
- the NDPA PPDU may include a PPDU header and a PSDU (or MPDU).
- the PPDU header may be used to mean a PHY preamble and a PHY header.
- the PSDU (or MPDU) of the NPDA PPDU may include an NDPA frame.
- the PPDU header of the NDPA PPDU includes a legacy short training field (L-STF) 500, a legacy long training field (L-LTF) 505, a legacy-signal (510) and a HE-SIG A.
- L-STF legacy short training field
- L-LTF legacy long training field
- HE-SIG A high efficiency-signal A
- HE-STF high efficiency-short training field
- HE-LTF high efficiency-long training field
- HE-SIG B high efficiency-signal
- the L-SIG 510 may be divided into a legacy part and a high efficiency (HE) part after the L-SIG 510.
- the L-STF 500 may include a short training orthogonal frequency division multiplexing symbol.
- the L-STF 500 may be used for frame detection, automatic gain control (AGC), diversity detection, and coarse frequency / time synchronization.
- AGC automatic gain control
- the L-LTF 505 may include a long training orthogonal frequency division multiplexing symbol.
- the L-LTF 505 may be used for fine frequency / time synchronization and channel prediction.
- the L-SIG 510 may be used to transmit control information.
- the L-SIG 510 may include information about a data rate and a data length.
- the HE-SIG A 515 may include information indicating an STA to receive the PPDU. In more detail, the HE-SIG A 515 may include information indicating an STA to receive an NDPA frame.
- the HE-SIG A 515 may include color bits information for BSS identification information, bandwidth information, tail bits, CRC bits, and an MCS for the HE-SIG B 530. It may include modulation and coding scheme information, symbol number information for the HE-SIG B 530, and cyclic prefix (CP) (or guard interval (GI)) length information.
- CP cyclic prefix
- GI guard interval
- the HE-STF 520 may be used to improve automatic gain control estimation in a multiple input multiple output (MIMO) environment or an OFDMA environment.
- MIMO multiple input multiple output
- OFDMA orthogonal frequency division multiple access
- the HE-LTF 525 may be used to estimate a channel in a MIMO environment or an OFDMA environment.
- the HE-SIG B 530 may include information on a length MCS of a physical layer service data unit (PSDU) for each STA, tail bits, and the like.
- PSDU physical layer service data unit
- the size of the inverse fast fourier transform (IFFT) applied to the fields after the HE-STF 520 and the HE-STF 520 may be different from the size of the IFFT applied to the field before the HE-STF 520.
- the size of the IFFT applied to the field after the HE-STF 520 and the HE-STF 520 may be four times larger than the size of the IFFT applied to the field before the HE-STF 520.
- the STA may receive the HE-SIG A 515 and may be instructed to receive the NDPA PPDU based on the HE-SIG A 515.
- the STA may perform decoding based on the FFT size changed from the field after the HE-STF 520 and the HE-STF 520.
- the STA may stop decoding and configure a network allocation vector (NAV).
- NAV network allocation vector
- the cyclic prefix (CP) of the HE-STF 520 may have a larger size than the CP of another field, and during this CP period, the STA may perform decoding on the downlink PPDU by changing the FFT size.
- the order of fields constituting the format of such an NDPA PPDU may be changed.
- HE-SIG B of the HE portion may be located immediately after HE-SIG A. That is, each field of the HE portion may be located in the order of HE-SIG A, HE-SIG B, HE-STF, and HE-LTF.
- the STA may decode up to HE-SIG A and HE-SIG B, receive necessary control information, and configure NAV.
- the size of the IFFT applied to the fields before the HE-STF and the HE-STF may be different from the size of the IFFT applied to the fields before the HE-STF.
- the STA may receive the HE-SIG A and the HE-SIG B.
- the STA may perform decoding on the downlink PPDU by changing the FFT size from the HE-STF.
- the STA may configure a network allocation vector (NAV).
- NAV network allocation vector
- the PSDU (or MPDU) 535 of the NDPA PPDU may include an NDPA frame.
- the NDPA frame includes a frame control field 540, a duration field 545, an RA field 550, a TA field 555, a sounding dialog token field 560, and an STA information field 565 and an FCS 570. can do.
- the frame control field 540 may include type and subtype information indicating an NDPA frame.
- the duration field 545 may include information on an interval for protecting transmission of the NDPA frame.
- the RA field 550 may include identification information of the STA to receive the NDPA frame.
- the RA field 550 may include address information of the STA when the STA information field includes information about one STA.
- the RA field 550 may include a broadcast address of the STA when the STA information field 565 includes information about the plurality of STAs.
- the RA field 550 may include MAC address information of the STA to receive the NDPA frame.
- the TA field 555 may include an address of an AP transmitting an NDPA frame.
- the sounding dialog token field 560 may include information for identifying an NDPA frame by an AP transmitting the NDPA frame.
- the STA information field 565 may include identification information (AID) 575, feedback type information 580, and Nc index information 585 of the STA to receive the NDPA frame.
- AID identification information
- feedback type information 580 feedback type information
- Nc index information 585 of the STA to receive the NDPA frame.
- Table 2 below discloses information included in the STA information field.
- Nc may indicate the number of columns of beamforming feedback matrices included in a feedback frame transmitted in response to the NDP.
- STAs that receive the NDPA frame may check the value of the AID subfield included in the STA information field and may determine whether the STA is a sounding target STA.
- the NDPA PPDU is a legacy PPDU format (e.g., HT PPDU format, VHT PPDU format) instead of HE-SIG A 515, HE-STF 520, HE-LTF 525, HE-SIG B 530. It may be.
- legacy PPDU format e.g., HT PPDU format, VHT PPDU format
- FIG. 6 is a conceptual diagram illustrating an NDP according to an embodiment of the present invention.
- the NDP (or PPDU header) may include a legacy portion and a non-legacy portion.
- Each field included in the legacy part and the non-legacy part may play the role described above with reference to FIG. 5 for transmission of the NDP.
- the HE-SIG A 600 may include information indicating an STA to receive an NDP.
- the HE-LTF 610 may be used for channel prediction of the STA. That is, the STA may perform channel prediction based on the HE-LTF 610 included in the NDP frame and generate a feedback frame based on the channel predicted result.
- the HE-SIG B 620 may include information indicating the length of the PSDU as zero.
- each field of the PPDU header may be located in the order of HE-SIG A, HE-SIG B, HE-STF, and HE-LTF.
- FIG. 7 is a conceptual diagram illustrating a feedback PPDU according to an embodiment of the present invention.
- the feedback PPDU may include a PPDU header and a PSDU (or MPDU).
- the PSDU (or MPDU) of the feedback PPDU may include a feedback frame.
- the PPDU header of the feedback PPDU may include a legacy part and a non-legacy part. Each field included in the legacy part and the non-legacy part may play the role described above in FIG. 5 for the feedback PPDU.
- the MAC header of the feedback frame may include an HT control field 700, and the MSDU may include a channel information control field 710 and a channel information field 720.
- the feedback frame is not included or reserved in the channel information control field 710 and the channel information field 720 and the feedback frame is HT. It may include only the control field 700. Only when beamforming is used in the sounding procedure, the feedback frame may include a channel information control field 710 and a channel information field 720.
- the HT control field 710 may include an MCS feedback (MFB) field, and the MFB field may include information on the number of recommended spatiotemporal streams (N_STS), information on a recommended MCS index (MCS), and a recommended MCS. It may include information on the intended bandwidth size (BW), information on all spatiotemporal streams that transmitted data, and average SNR measured on the subcarriers.
- MFB MCS feedback
- N_STS number of recommended spatiotemporal streams
- MCS recommended MCS index
- BW intended bandwidth size
- Tables 3 and 4 show the formats of the channel information control field 710 and the channel information field 720.
- Table 3 below discloses information included in the channel information control field 710.
- Table 4 below discloses information included in the channel information field 720.
- Information of the channel information field 720 described in Table 4 may be interpreted based on information included in the channel control field 710 described in Table 3.
- the AP may receive a feedback frame and the subcarrier index Ns may be determined based on the channel bandwidth information and the grouping information of the channel information control field 710.
- an SNR or a beamforming feedback matrix (or a matrix vector) for the entire frequency band may be transmitted through the feedback PPDU.
- FIG. 8 is a conceptual diagram illustrating a frame transmission method based on a sounding procedure according to an embodiment of the present invention.
- FIG. 8 illustrates a frame transmission method based on a sounding procedure for a plurality of STAs.
- a sounding procedure is disclosed.
- the AP may transmit the NDPA frame 800 to the STA for the sounding procedure and transmit the NDP 810 after a predetermined time (eg, SIFS).
- a predetermined time eg, SIFS
- the NDPA frame 800 and the NDP 810 may be transmitted in a non-duplicate format or in a duplicate format in the entire transmission band for the NDPA frame 800 and the NDP 810 as described above in FIG. 4.
- the LTF is transmitted through a plurality of space-time streams through the NDP 810, and each of the plurality of STAs may transmit a feedback frame including channel state information measured based on the indicated space-time stream and the LTF of the indicated frequency domain to the AP. have.
- the NDP 810 may indicate UL MU transmission of feedback frames by a plurality of STAs.
- Each of the plurality of STAs may transmit a feedback frame to the AP after a predetermined time (eg, SIFS) based on the reception of the NDP 810.
- a predetermined time eg, SIFS
- Each of the plurality of STAs may receive the NDPA frame 800 and the NDP 810 and transmit a feedback frame 820 to the AP based on a UL MU transmission method.
- each of the plurality of STAs may transmit a feedback frame on the overlapped time resource through the allocated space-time stream or frequency resource.
- the AP may receive the feedback frame 820 transmitted based on the UL MU transmission from each of the plurality of STAs. That is, the AP may receive each of a plurality of feedback frames transmitted through each of a plurality of transmission resources allocated to each of the plurality of STAs on time resources overlapped by each of the plurality of STAs.
- Each of the plurality of STAs may receive the downlink frame 830 and transmit an ACK or a block ACK for the downlink frame 830 to the AP based on the UL MU transmission.
- the AP may transmit the downlink frame 830 based on the DL MU to each STA that has transmitted the feedback frame 820, but the downlink frame 830 may be transmitted to some STAs among all the STAs which have transmitted the feedback frame 820. Can also be transmitted. For example, the AP may not transmit the downlink frame 830 to some of all STAs that have transmitted the feedback frame 820 in consideration of the channel state information included in the feedback frame 820. . In this case, the AP may instruct the STA to receive the downlink frame 830 based on the downlink PPDU carrying the downlink frame 830. For example, the HE-SIG A field included in the PPDU header of the downlink PPDU may include information indicating an STA to receive.
- the information indicating the STA to receive the downlink PPDU may be an index indexing the AIDs of the STAs included in the NDPA frame 800 in order. For example, the first AID may be mapped to index 0 and the second AID may be mapped to index 1.
- An STA to receive the downlink PPDU may be indicated based on an index value corresponding to the AID included in the downlink PPDU.
- an STA to receive the downlink frame 830 may be indicated based on the group ID.
- FIG. 9 is a conceptual diagram illustrating a frame transmission method based on a sounding procedure according to an embodiment of the present invention.
- FIG. 9 illustrates a frame transmission method based on a sounding procedure for a plurality of STAs.
- FIG. 9 discloses a case in which both DL MU transmission and UL MU transmission are supported and the number of STAs instructed to transmit the feedback frame in the sounding procedure is larger than the maximum number of STAs that can be transmitted based on the UL MU transmission.
- the AP may transmit the NDPA frame 900 to the plurality of STAs for the sounding procedure and may transmit the NDP 910 after a predetermined time (eg, SIFS).
- a predetermined time eg, SIFS
- the NDPA frame 900 and the NDP 910 in the non-duplicate PPDU format or the duplicate PPDU format may be transmitted to at least one STA through at least one space-time stream.
- the AP may transmit the NDPA frame 900 and the NDP 910 to the plurality of STAs through the plurality of space-time streams.
- the NDPA frame 900 may indicate a plurality of STAs for transmitting a feedback frame.
- the LTF is transmitted through a plurality of space-time streams through the NDP 910, and each of the plurality of STAs may transmit a feedback frame including channel state information measured based on the indicated space-time stream and the LTF of the indicated frequency domain to the AP. have.
- the NDPA frame 900 may instruct the transmission of the feedback frames 920 and 940 to more STAs than the maximum number of STAs that can be transmitted based on the UL MU transmission.
- the number of STAs indicated based on the STA information field of the NDPA frame 900 may be larger than the maximum number of STAs that can be transmitted based on UL MU transmission.
- the NDP 910 may indicate UL MU transmission of the feedback frame 920 by the plurality of STAs.
- the NDP 910 may be received by more STAs than the number of STAs that can be transmitted based on UL MU transmission.
- the AP may receive feedback frames from the plurality of STAs based on polling. For example, when more than N STAs are instructed to perform a sounding procedure based on the NDPA frame 900 and the maximum number of STAs that can be transmitted based on UL MU transmission is N, N STAs are NDP (910). ), And after SIFS, the feedback frame 920 may be transmitted based on the UL MU transmission. The remaining STA may transmit a feedback frame 940 based on the polling frame 930 transmitted by the AP.
- the transmission priority of the feedback frames 920 and 940 may be determined based on the order of the AIDs of the STA information fields included in the NDPA frame 900. For example, a plurality of STAs corresponding to N AIDs included in priority among the AIDs of the STA information field may transmit the feedback frame 920 to the AP after receiving the NDP 910. The STA corresponding to the remaining AID may receive the polling frame 930 from the AP and transmit a feedback frame 940 to the AP.
- the AP is based on feedback frames 920 and 940 received from the plurality of STAs (when the number of STAs capable of transmitting DL MU is greater than or equal to the number of STAs transmitting feedback information) or a part of the plurality of STAs (DL
- the downlink frame 950 may be transmitted based on the DL MU transmission method for the number of STAs capable of transmitting MUs is smaller than the number of STAs transmitting feedback information.
- the PPDU header of the downlink PPDU that transmits the downlink frame transmitted based on the DL MU transmission may indicate an STA to receive the downlink PPDU. Accordingly, the plurality of STAs that have transmitted the feedback frame may determine whether to receive (or further decode) the downlink frame 950 based on the PPDU header information of the downlink PPDU carrying the downlink frame 950.
- FIG. 10 is a conceptual diagram illustrating a frame transmission method based on a sounding procedure according to an embodiment of the present invention.
- FIG. 10 a method of transmitting a frame based on a sounding procedure for a plurality of STAs is disclosed. 10 particularly discloses the case where only the DL MU transmission method is supported.
- the AP may transmit the NDPA frame 1000 to the STA for the sounding procedure and transmit the NDP 1010 after a predetermined time (eg, SIFS).
- a predetermined time eg, SIFS
- the NDPA frame 1000 and the NDP 1010 in the non-duplicate PPDU format or the duplicate PPDU format may be transmitted to at least one STA through at least one space-time stream.
- the AP may transmit the NDPA frame 1000 and the NDP 1010 to the plurality of STAs through the plurality of space-time streams.
- the NDPA frame 1000 may indicate a plurality of STAs for transmitting a feedback frame.
- the LTF is transmitted through a plurality of space-time streams through the NDP 1010, and each of the STAs may transmit a feedback frame including channel state information measured based on the indicated space-time stream and the LTF of the indicated frequency domain to the AP.
- the NDP 1010 may instruct transmission of a feedback frame 1015 of one of a plurality of STAs indicated based on the NDPA frame 1000.
- an STA corresponding to the first AID of the AIDs included in the STA information field of the NDPA frame 1000 may receive the NDP 1010 and transmit a feedback frame to the AP for a predetermined time (for example, after SIFS). .
- At least one STA corresponding to the remaining AID may sequentially receive polling frames 1020 and 1030 from the AP and transmit feedback frames 1015 and 1025 to the AP.
- the AP may receive feedback frames 1015 and 1025 from a plurality of STAs, determine channel variable information, and transmit a downlink frame 1040 based on a DL MU transmission method.
- the plurality of STAs receiving the downlink frame 1040 transmitted based on the DL MU transmission method may be all or part of the plurality of STAs transmitting the feedback frames 1015 and 1025.
- 11 to 12 specifically describe the format of an NDPA PPDU, NPD carrying an NDPA frame for performing another sounding procedure in an embodiment of the present invention.
- FIG. 11 is a conceptual diagram illustrating a format of an NDPA PPDU according to an embodiment of the present invention.
- FIG. 11 discloses an NDPA PPDU transmitted to each of a plurality of STAs through different downlink transmission resources (frequency resources or spatial streams).
- NDPA frames transmitted through different space-time streams or different frequency resources may include information that is not identical.
- the NDPA PPDU may be transmitted to the plurality of STAs through the entire band allocated based on the non-duplicate format or transmitted to the plurality of STAs through the plurality of channels based on the duplicate format.
- the above-described NDPA PPDU format of FIG. 5 is used, and the HE-SIG A field may indicate a plurality of STAs.
- the previous field of the HE-SIG B 1110 on the NDPA PPDU may be transmitted in duplicated form in each of different downlink transmission resources.
- the HE-SIG B 1110 may be transmitted in an encoded form on all transmission resources.
- the field after the HE-SIG B 1110 may include individual information for each of the plurality of STAs that receive the NDPA PPDU.
- the field after the HE-SIG B 1110 transmitted through the first transmission resource includes an STA information field indicating STA1 and after the HE-SIG B 1110 transmitted through the second transmission resource.
- the field of may include a STA information field indicating STA2.
- the NDPA PPDU may include an HE-SIG B 1110 in an encoded form on all transmission resources. When HE-SIG B 1110 of this format is used, CRC overhead can be reduced.
- the HE-SIG A 1100 of the NDPA PPDU includes information indicating a plurality of STAs to receive the NDPA PPDU and / or information about transmission resources for receiving NDPA PPDUs of each of the plurality of STAs assigned to each of the plurality of STAs. can do. That is, the HE-SIG A 1100 may include information about transmission resources allocated to each of the plurality of STAs. Each of the plurality of STAs may receive an NDPA PPDU through a transmission resource indicated based on the HE-SIG A 1100.
- Downlink frames (downlink data frames, downlink management frames) transmitted based on the DL MU transmission disclosed in the embodiment of the present invention are also transmitted to a plurality of STAs based on the same PPDU format as the NDPA PPDU format disclosed in FIG. 11. Can be sent.
- FIG. 12 is a conceptual diagram illustrating an NDP according to an embodiment of the present invention.
- the NDP may include only a PPDU header excluding a PSDU (or MPDU).
- NDP transmitted to each of a plurality of STAs through different downlink transmission resources (frequency resources or spatial streams). NDPs transmitted through different space-time streams or different frequency resources may include unequal information.
- the NDP may include a legacy portion and a non-legacy portion.
- Each field included in the legacy part and the non-legacy part may play the role described above with reference to FIG. 5.
- the field before the HE-SIG B 1210 may be transmitted in a duplicated form in each of different downlink transmission resources.
- the HE-SIG B 1210 may be transmitted in an encoded form on all transmission resources.
- the field after the HE-SIG B 1210 may include individual information for each of the plurality of STAs receiving the NDPA PPDU.
- the HE-SIG A 1200 may include information indicating a plurality of STAs to receive an NDP and information about transmission resources allocated to each of the plurality of STAs. Each of the plurality of STAs may receive an NDP through a transmission resource indicated based on the HE-SIG A.
- Each of the STAs may generate feedback information by receiving the HE-LTF transmitted through the indicated transmission resource based on the indicated HE-SIG A 1200 and performing channel prediction.
- FIG. 13 is a conceptual diagram illustrating a PPDU format for a sounding procedure according to an embodiment of the present invention.
- FIG. 13 a sounding procedure based on one PPDU is disclosed.
- a new sounding PPDU including a training field (eg, HE-LTF2 1300) for channel measurement may be defined after the NDPA PPDU.
- the new sounding PPDU having added the training field 1300 for channel measurement after the NDPA PPDU may be defined in terms of synthesized sounding PPDU.
- a separate NDP may not be transmitted.
- the NDP is transmitted in a format of a null frame that does not include a training field (for example, HE-LTF). It may be.
- the STA may generate channel state information based on the synthesized sounding PPDUs without performing separate decoding on the NDP and may include the generated channel state information in a feedback frame and transmit the same.
- FIG. 14 is a conceptual diagram illustrating a PPDU format for transmitting an ACK frame according to an embodiment of the present invention.
- FIG. 14 discloses a PPDU carrying an UL MU based ACK frame.
- the UL MU based ACK frame disclosed in FIG. 14 may be used for transmission of UL MU based ACK or block ACK of a plurality of STAs described above.
- each subband may be a frequency resource that may be allocated to each STA for OFDMA based transmission.
- a frequency band of 20 MHz may include four 5 MHz subbands. Each of the four 5 MHz subbands may be used for OFDMA-based DL MU transmission to a plurality of STAs.
- the UL MU ACK frame may be transmitted in response to the plurality of downlink PPDUs transmitted based on the DL MU transmission.
- a PPDU carrying a UL MU ACK frame may include a HE portion.
- the HE portion may include an HE-STF 1400, an HE-SIG field 1410, and an HE-ACK data field 1420.
- the UL MU ACK PPDU may include an HE portion (HE-STF 1400, HE-SIG field 1410) as a PPDU header, and may include an ACK frame 1420 as a PSDU (or MPDU).
- An OFDM symbol for transmission of each field included in the UL MU ACK PPDU may include an extended CP.
- the UL MU ACK PPDU may include legacy portions (L-STF, L-LTF, and L-SIG), but may have a format not including the legacy portions as shown in FIG. 14.
- the length of the extended CP may be two or four times the length of the CP of the OFDM symbol for transmission of the HE-STF and the HE-SIG included in the downlink PPDU transmitted through the DL MU.
- the HE-STF and the HE-SIG are transmitted on overlapping frequency resources (or frequency bands including all subbands) on overlapping time resources, and the remaining ACK data (or ACK frames) are allocated per STA. It can be transmitted over frequency resources. That is, the AP may receive a plurality of acknowledgment (ACK) data for each of the plurality of downlink frames through each of the plurality of transmission resources allocated from each of the plurality of STAs to each of the plurality of STAs on the overlapped time resources. In this case, the training field and the signal field for decoding each of the plurality of ACK data may be transmitted through a plurality of transmission resources.
- ACK acknowledgment
- each of the STA1 to STA4 has a HE-STF through a 20 MHz band, which is a frequency band including all subbands.
- HE-SIG may be transmitted, and ACK data may be transmitted through subbands of 5 MHz each allocated.
- the HE-STF, HE-SIG, and ACK data may be transmitted in the UL MU ACK PPDU through allocated frequency resources.
- the HE-STF, HE-SIG, and ACK data may be transmitted.
- a SIG field or a control field of a downlink PPDU that transmits a downlink frame based on a DL MU MIMO transmission to transmit ACK PPDUs from a plurality of STAs based on UL MU MIMO transmission may include information for UL MU MIMO transmission.
- the information for UL MU MIMO transmission may include resource allocation information (eg, space-time stream indication information) that each of the plurality of STAs will use to transmit the ACK frame.
- the UL MU MIMO method to be used for transmitting ACK frames of a plurality of STAs may be determined or predetermined (or promised) based on the DL MU MIMO method used to transmit the downlink frame (eg, beacon frame). May be determined in consideration of the information signaled by or a predetermined method).
- 15 is a block diagram illustrating a wireless device to which an embodiment of the present invention can be applied.
- the wireless device 1500 may be an STA that may implement the above-described embodiment and may be an AP 1500 or a non-AP station (or STA) 1550.
- the AP 1500 includes a processor 1510, a memory 1520, and an RF unit 1530.
- the RF unit 1530 may be connected to the processor 1510 to transmit / receive a radio signal.
- the processor 1510 may implement the functions, processes, and / or methods proposed in the present invention.
- the processor 1510 may be implemented to perform the operation of the AP according to the above-described embodiment of the present invention.
- the processor may perform the operation of the AP disclosed in the embodiments of FIGS. 1 to 14.
- the RF unit 1580 may be connected to the processor 1560 to transmit / receive a radio signal.
- the processor 1560 may implement the functions, processes, and / or methods proposed in the present invention.
- the processor 1520 may be implemented to perform the operation of the STA according to the embodiment of the present invention described above.
- the processor may perform the operation of the STA in the embodiments of FIGS. 1 to 14.
- the processor 1560 may receive an NDP from the AP, perform channel measurement, and transmit a feedback frame to the AP based on a UL MU transmission method.
- Processors 1510 and 1560 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, data processing devices, and / or converters for interconverting baseband signals and wireless signals.
- the memories 1520 and 1570 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices.
- the RF unit 1530 and 1580 may include one or more antennas for transmitting and / or receiving a radio signal.
- the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function.
- the module may be stored in the memories 1520 and 1570 and executed by the processors 1510 and 1560.
- the memories 1520 and 1570 may be inside or outside the processors 1510 and 1560, and may be connected to the processors 1510 and 1560 by various well-known means.
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Abstract
Description
Claims (8)
- 무선랜에서 사운딩 절차 기반의 프레임 전송 방법에 있어서,
AP(access point)가 복수의 STA(station) 각각으로 NDPA(null data packet announcement) 프레임을 전송하되, 상기NDPA 프레임은 NDP(null data packet)의 전송을 알리는, 단계;
상기 AP가 상기 복수의 STA 각각으로 상기 NDP를 전송하는 단계;
상기 AP가 상기 복수의 STA 각각에 의해 중첩된 시간 자원 상에서 상기 복수의 STA 각각으로 할당된 복수의 전송 자원 각각을 통해 전송되는 복수의 피드백 프레임 각각을 수신하는 단계; 및
상기 AP가 상기 복수의 STA 각각으로 복수의 하향링크 프레임 각각을 전송하는 단계를 포함하되,
상기 복수의 피드백 프레임 각각은 상기 NDP를 기반으로 결정된 복수의 채널 상태 정보 각각을 포함하고,
상기 복수의 하향링크 프레임 각각은 상기 복수의 피드백 프레임 각각의 수신 후 일정 시간 이내에 상기 복수의 채널 상태 정보 각각을 기반으로 전송되는 방법. - 제1항에 있어서,
상기 NDPA 프레임은 STA 정보 필드를 포함하고,
상기 STA 정보 필드는 상기 복수의 STA 각각의 식별자 정보를 포함하는 것을 특징으로 하는 방법. - 제1항에 있어서,
상기 AP가 중첩된 시간 자원 상에서 상기 복수의 STA 각각으로부터 상기 복수의 STA 각각으로 할당된 복수의 전송 자원 각각을 통해 상기 복수의 하향링크 프레임 각각에 대한 복수의 ACK(acknowledgement) 데이터 각각을 수신하는 단계를 포함하되,
상기 복수의 ACK 데이터 각각의 디코딩을 위한 트레이닝 필드 및 시그널 필드는 상기 복수의 전송 자원을 통해 전송되는 것을 특징으로 하는 방법. - 제1항에 있어서,
상기 일정 시간은 SIFS(short interframe space)인 것을 특징으로 하는 방법. - 무선랜에서 사운딩 절차를 기반의 프레임을 전송하는 AP(access point)에 있어서, 상기 AP는
무선 신호를 송신 또는 수신하기 위해 구현되는 RF(radio frequency) 부; 및
상기 RF부와 동작 가능하게(operatively) 연결된 프로세서를 포함하되,
상기 프로세서는 복수의 STA(station) 각각으로 NDPA(null data packet announcement) 프레임을 전송하되, 상기 NDPA 프레임은 NDP(null data packet)의 전송을 알리고,
상기 복수의 STA 각각으로 상기 NDP를 전송하고,
상기 복수의 STA 각각에 의해 중첩된 시간 자원 상에서 상기 복수의 STA 각각으로 할당된 복수의 전송 자원 각각을 통해 전송되는 복수의 피드백 프레임 각각을 수신하고,
상기 복수의 STA 각각으로 복수의 하향링크 프레임 각각을 전송하도록 구현되되,
상기 복수의 피드백 프레임 각각은 상기 NDP를 기반으로 결정된 복수의 채널 상태 정보 각각을 포함하고,
상기 복수의 하향링크 프레임 각각은 상기 복수의 피드백 프레임 각각의 수신 후 일정 시간 이내에 상기 복수의 채널 상태 정보 각각을 기반으로 전송되는 AP. - 제5항에 있어서,
상기 NDPA 프레임은 STA 정보 필드를 포함하고,
상기 STA 정보 필드는 상기 복수의 STA 각각의 식별자 정보를 포함하는 것을 특징으로 하는 AP. - 제5항에 있어서,
상기 프로세서는 중첩된 시간 자원 상에서 상기 복수의 STA 각각으로부터 상기 복수의 STA 각각으로 할당된 복수의 전송 자원 각각을 통해 상기 복수의 하향링크 프레임 각각에 대한 복수의 ACK(acknowledgement) 데이터 각각을 수신하도록 구현되되,
상기 복수의 ACK 데이터 각각의 디코딩을 위한 트레이닝 필드 및 시그널 필드는 상기 복수의 전송 자원을 통해 전송되는 것을 특징으로 하는 AP. - 제5항에 있어서,
상기 일정 시간은 SIFS(short interframe space)인 것을 특징으로 하는 AP.
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