Method for transmitting sounding signal in wireless communication system

1. A method for allowing a station to transmit a sounding signal in a multiple-antenna wireless communication system, the method comprising

receiving, by the station, a first frame including a group defining field from an access point (AP), the group defining field including information on a group identifier of a plurality of stations being receivers of a multi user (MU)-multiple input multiple output (MIMO) transmission of the AP, the plurality of the stations including the station;

receiving, by the station, a second frame including a training request (TRQ) field and an antenna field, the TRQ field including information on triggering each transmission of sounding physical layer protocol data units (PPDUs) of each of the plurality of the stations for a channel estimation between the AP and the each of the plurality of the stations and the antenna field including information on a number of antennas of the each of the plurality of the stations used to transmit each of the sounding PPDUs;

determining, by the station, a transmission time of a sounding PPDU based on the antenna field; and

transmitting, by the station, the sounding PPDU to the AP based on the transmission time,

wherein the group defining field further includes information on a transmission order of the sounding PPDU and each of at least one sounding PPDU transmitted by each of at least one remaining station without the station included in the plurality of the stations,

wherein the transmission time increases proportional to a sum of a number of antennas of at least one station among the at least one remaining station transmitting another sounding PPDU before the station transmits the sounding PPDU when the station is configured to wait a minimum time to transmit the sounding PPDU,

wherein the number of antennas of the at least one station is determined based on the information on the transmission order and the antenna field,

wherein the transmission time increases proportional to a maximum number of layers supported by the AP when the station is configured to wait a maximum time to transmit the sounding PPDU, and

wherein a number of long training fields (LTFs) in the sounding PPDU is determined based on information on the number of antennas of the station included in the antenna field.

2. A station (STA) to transmit a sounding signal in a multiple-antenna wireless communication system, the STA comprising:

a RF(radio frequency) unit configured to transmit or receive a radio signal; and

a processor operatively connected to the RF unit and configured to receive a first frame including a group defining field from an access point (AP), the group defining field including information on a group identifier of a plurality of stations being receivers of a multi use(MU)-multiple input multiple output (MIMO) transmission of the AP, the plurality of the stations including the station,

receive a second frame including a training request (TRQ) field and an antenna field, the TRQ field including information on triggering each transmission of sounding physical layer protocol data units (PPDUs) of each of the plurality of the stations for a channel estimation between the AP and the each of the plurality of the stations and the antenna field including information on a number of antennas of the each of the plurality of the stations used to transmit each of the sounding PPDUs,

determine a transmission time of a sounding PPDU based on the antenna field, and

transmit the sounding PPDU to the AP based on the transmission time,

wherein the group defining field further includes information on a transmission order of the sounding PPDU and each of at least one sounding PPDU transmitted by each of at least one remaining station without the station included in the plurality of the stations,

wherein the transmission time increases proportional to a sum of a number of antennas of at least one station among the at least one remaining station transmitting another sounding PPDU before the station transmits the sounding PPDU when the station is configured to wait a minimum time to transmit the sounding PPDU,

wherein the number of antennas of the at least one station is determined based on the information on the transmission order and the antenna field,

wherein the transmission time increases proportional to a maximum number of layers supported by the AP when the station is configured to wait a maximum time to transmit the sounding PPDU, and

wherein a number of long training fields (LTFs) in the sounding PPDU is determined based on information on the number of antennas of the station included in the antenna field.

3. A method for a sounding procedure, the method comprising:

transmitting, by an access point (AP), a first frame including a group defining field to a plurality of stations, the group defining field including information on an group identifier of the plurality of stations being receivers of multi user (MU)-multiple input multiple output (MIMO) transmission of the AP;

transmitting, by the AP, a second frame including a training request (TRQ) field and an antenna field, the TRQ field including information on triggering each transmission of sounding physical layer protocol data units (PPDUs) of each of the plurality of the stations for a channel estimation between the AP and the each of the plurality of the stations and the antenna field including information on a number of antennas of the each of the plurality of the stations used to transmit each of the sounding PPDUs; and

receiving, by the AP, each of the sounding PPDUs from the each of the plurality of stations sequentially as responses of the second frame,

wherein the group defining field further includes information on a transmission order of the sounding PPDUs,

wherein the each of the sounding PPDUs is received based on each of the transmission times of the each of the sounding PPDUs,

wherein the transmission times of the each of the sounding PPDUs is determined based on the transmission order and the number of antennas of the each of the plurality of stations when the station is configured to wait a minimum time to transmit the sounding PPDU,

wherein the transmission times of the each of sounding PPDU is determined based on a maximum number of layers supported by the AP when the station is configured to wait a maximum time to transmit the sounding PPDU, and

wherein each of a number of long training fields (LTFs) in the each of the sounding PPDUs is determined based on information on the number of antennas of the each of the plurality of the stations used to transmit the each of the sounding PPDUs.

4. An access point (AP) for a sounding procedure, the AP comprising:

a RF(radio frequency) unit configured to transmit or receive a radio signal; and

a processor operatively connected to the RF unit and configured to:

transmit a first frame including a group defining field to a plurality of stations, the group defining field including information on an group identifier of the plurality of stations being receivers of multi user (MU)-multiple input multiple output (MIMO) transmission of the AP,

transmit a second frame including a training request (TRQ) field and an antenna field, the TRQ field including information on triggering each transmission of sounding physical layer protocol data units (PPDUs) of each of the plurality of the stations for a channel estimation between the AP and the each of the plurality of the stations and the antenna field including information on a number of antennas of the each of the plurality of the stations used to transmit each of the sounding PPDUs, and

receive each of the sounding PPDUs from the each of the plurality of stations sequentially as responses of the second frame,

wherein the group defining field further includes information on a transmission order of the sounding PPDUs,

wherein the each of the sounding PPDUs is received based on each of the transmission times of the each of the sounding PPDUs,

wherein the transmission times of the each of the sounding PPDUs is determined based on the transmission order and the number of antennas of the each of the plurality of stations when the station is configured to wait a minimum time to transmit the sounding PPDU,

wherein the transmission times of the each of sounding PPDU is determined based on a maximum number of layers supported by the AP when the station is configured to wait a maximum time to transmit the sounding PPDU, and

wherein each of a number of long training fields (LTFs) in the each of the sounding PPDUs is determined based on information on the number of antennas of the each of the plurality of the stations used to transmit the each of the sounding PPDUs.