Patent ID: 9525474
Filing Date: 2016-12-20
CPC Classification: H04B,H04L,H04W

Claim Text:
1. A method for performing channel sounding in a wireless LAN system, the method comprising the steps of: transmitting a null data packet announcement (NDPA) frame to announce a transmission of a null data packet (NDP); transmitting the NDP; and receiving a feedback frame from a station (STA), wherein the feedback frame includes channel state information generated based on the NDP, wherein the NDP includes a signal field, a first long training field (LTF) used in channel estimation for decoding the signal field and a second LTF used in channel estimation for a multiple input multiple output (MIMO) channel, wherein the signal field includes a repetition indication subfield, wherein the repetition indication subfield indicates whether orthogonal frequency division multiplexing (OFDM) symbol repetition is applied to the second LTF, wherein the first LTF is transmitted as an OFDM symbol for the first LTF and as a repetition OFDM symbol in which the first LTF is repeated regardless of the repetition indication subfield, and wherein when the repetition indication subfield indicates that the OFDM symbol repetition is not applied to the second LTF, the second LTF is transmitted as a first long training symbol (LTS) for each LTF.