SOUNDING METHOD
A sounding method of a receiving device is provided. The receiving device receives an NDPA frame and then receives an NDP frame, from a transmitting device. After receiving the NDP frame, the receiving device transmits to the transmitting device a channel feedback frame including feedback information according to a feedback type indicated by the feedback type information.
1 . A sounding method of a receiving device, the method comprising:
receiving a null data packet announcement (NDPA) frame including feedback type information from a transmitting device;
receiving a null data packet (NDP) frame from the transmitting device after receiving the NPDA frame; and
transmitting to the transmitting device a channel feedback frame including feedback information according to a feedback type indicated by the feedback type information after receiving the NDP frame.
2 . The method of claim 1 , wherein the NDPA frame further includes grouping information indicating how many subcarriers are grouped to be fed back as single information.
3 . The method of claim 2 , wherein, when the grouping information indicates that N subcarriers are grouped to be fed back as the single information, in a long training field of the NDP frame, a value for the long training field is transmitted through only one subcarrier among the N subcarriers.
4 . The method of claim 2 , wherein, when the grouping information indicates that N subcarriers are grouped to be fed back as the single information, in a long training field of the NDP frame, values for different transmitting antennas are transmitted through the Ng subcarriers, respectively.
5 . The method of claim 1 , wherein the NDPA frame further includes size information of a fast Fourier transform (FFT) used in a part of the NDP frame or length information of a guard interval used in the part of the NDP frame.
6 . The method of claim 5 , wherein the part of the NDP frame includes a long training field of the NDP frame.
7 . The method of claim 1 , wherein the NDPA frame further includes codebook information,
wherein the feedback information includes beamforming feedback matrix information that is provided in a form of angles that are determined based on a quantization level indicated by the codebook information, and
wherein the beamforming feedback matrix information is used for determining a matrix for multiple input multiple output (MIMO) transmission.
8 . The method of claim 1 , wherein, when the feedback type indicated by the feedback type information is orthogonal frequency division multiple access (OFDMA) transmission, the feedback information, when a predetermined band is divided into a plurality of subchannels, includes an average signal-to-noise ratio (SNR) for each of the subchannels.
9 . The method of claim 8 , further comprising:
receiving from the transmitting device a second NDPA frame including feedback type information indicating MIMO transmission;
receiving a second NDP frame from the transmitting device after receiving the second NPDA frame; and
transmitting to the transmitting device a second channel feedback frame including feedback information for the MIMO transmission after receiving the second NDP frame,
wherein the feedback information includes beamforming feedback matrix information at a subchannel that is allocated to the receiving device among the plurality of subchannels, and the beamforming feedback matrix information is used for determining a matrix for the MIMO transmission.
10 . The method of claim 9 , wherein, when the MIMO transmission is multi-user MIMO (MU-MIMO) transmission, the feedback information further includes SNR information per subcarrier for each stream, and
wherein the matrix for the MU-MIMO transmission is determined based on the beamforming feedback matrix information and the SNR information per subcarrier.
11 . The method of claim 9 , wherein the second NDP frame includes information on a subchannel allocated to the receiving device.
12 . The method of claim 1 , wherein, when the feedback type indicated by the feedback type information is OFDMA and MIMO transmission, the feedback information, when a predetermined band is divided into a plurality of subchannels, includes an average SNR for each subchannel and beamforming feedback matrix information for each subchannel, and
wherein the beamforming feedback matrix information is used for a matrix for the MIMO transmission.
13 . The method of claim 12 , wherein, when the MIMO transmission is MU-MIMO transmission, the feedback information further includes SNR information per subcarrier for each stream, and
wherein the matrix for the MU-MIMO transmission is determined based on the beamforming feedback matrix information and the SNR information per subcarrier.
14 . A sounding method of a transmitting device, the method comprising:
transmitting to a plurality of receiving devices a null data packet announcement (NDPA) frame including a plurality of feedback type information;
transmitting a null data packet (NDP) frame to the plurality of devices after transmitting the NPDA frame; and
receiving from the plurality of receiving devices channel feedback frames, each of the channel feedback frames including feedback information according to a feedback type indicated by corresponding feedback type information.
15 . The method of claim 14 , wherein the NDPA frame further includes grouping information indicating how many subcarriers are grouped to be fed back as single information.
16 . The method of claim 14 , wherein the NDPA frame further includes size information of a fast Fourier transform (FFT) used in a part of the NDP frame or length information of a guard interval used in the part of the NDP frame.
17 . The method of claim 14 , wherein the NDPA frame further includes a plurality of codebook information respectively corresponding to the plurality of receiving devices,
wherein the feedback information includes beamforming feedback matrix information that is provided in a form of angles that are determined based on a quantization level indicated by a corresponding codebook information among the plurality of codebook information, and
wherein the beamforming feedback matrix information is used for determining a matrix for multiple input multiple output (MIMO) transmission.
18 . The method of claim 14 , wherein, when the feedback type indicated by the corresponding feedback type information is orthogonal frequency division multiple access (OFDMA) transmission, the feedback information, when a predetermined band is divided into a plurality of subchannels, includes an average signal-to-noise ratio (SNR) for each of the subchannels.
19 . The method of claim 18 , further comprising:
transmitting to the plurality of receiving devices a second NDPA frame including feedback type information indicating MIMO transmission;
transmitting a second NDP frame to the plurality of receiving devices after transmitting the second NPDA frame; and
receiving from the plurality of receiving devices second channel feedback frames each including feedback information for the MIMO transmission,
wherein the feedback information includes beamforming feedback matrix information at a subchannel that is allocated to a corresponding receiving device among the plurality of subchannels, and the beamforming feedback matrix information is used for determining a matrix for the MIMO transmission.
20 . The method of claim 14 , wherein, when the feedback type indicated by the corresponding feedback type information is OFDMA and MIMO transmission, the feedback information, when a predetermined band is divided into a plurality of subchannels, includes an average SNR for each subchannel and beamforming feedback matrix information for each subchannel, and
wherein the beamforming feedback matrix information is used for a matrix for the MIMO transmission.