Frame transmitting method and frame receiving method

1. A method of transmitting a frame by a device in a wireless communication network, the method comprising:

generating a first symbol having a first subcarrier spacing, a symbol duration of the first symbol, excluding a guard interval, having a first length;

generating a second symbol having a second subcarrier spacing narrower than the first subcarrier spacing, a symbol duration of the second symbol, excluding a guard interval, having a second length that is twice the first length;

generating a third symbol, a symbol duration of the third symbol, excluding a guard interval, having a third length that is twice the second length; and

transmitting a frame including the first symbol, the second symbol, and the third symbol,

wherein the frame includes a legacy preamble part, a HE (high efficiency) long training field that is adapted for use in channel estimation, and a data field,

wherein the legacy preamble part includes the first symbol, the HE long training field includes the second symbol, and the data field includes the third symbol,

wherein a basic bandwidth of the frame is divided into a plurality of subbands,

wherein the data field is encoded per each subband and transmitted,

wherein the data field transmitted on a first subband includes data for a first receiving device allocated to the subband, and

the method further including:

forming a guard band between the first subband and a second subband in response to the second subband being allocated to a second receiving device, and

not forming a guard band between the first subband and the second subband in response to the second subband being allocated to the first receiving device,

wherein the second subband is adjacent to the first subband.

2. The method of claim 1 , wherein the first length is 3.2 μs and the second length is 6.4 μs.

3. The method of claim 1 , wherein generating the second symbol includes:

performing an inverse Fourier transform by using only even-numbered subcarriers among the plurality of subcarriers; and

using only one period of two periods that are output by the inverse Fourier transform.

4. The method of claim 1 , wherein the third length is 12.8 μs.

5. The method of claim 1 , wherein the frame further includes a first HE signal field and a second HE signal field that both follow the legacy preamble part, and

wherein the second HE signal field is encoded per the basic bandwidth and transmitted, and includes allocation information of the subbands.

6. The method of claim 5 , wherein the second HE signal field further includes information on devices that receive the frame on each subband.

7. The method of claim 1 , wherein the basic bandwidth is 20 MHz.

8. The method of claim 1 , wherein the legacy preamble part further includes a legacy signal field, and

wherein two symbols that immediately follow the legacy signal field are modulated by using BPSK (binary phase shift keying) modulation.

9. A method of receiving a frame by a device in a wireless communication network, the method comprising:

detecting in a frame a first symbol having a first subcarrier spacing, a second symbol having a second subcarrier spacing narrower than the first subcarrier spacing, and a third symbol, a symbol duration of the first symbol, excluding a guard interval, having a first length, a symbol duration of the second symbol, excluding a guard interval, having a second length that is twice the first length, and a symbol duration of the third symbol, excluding a guard interval, having a third length that is twice the second length; and

processing the first symbol, the second symbol, and the third symbol in the frame,

wherein the frame includes a legacy preamble part, a long training field that follows the legacy preamble part and is adapted for use for channel estimation, and a data field,

wherein the legacy preamble part includes the first symbol, the long training field includes the second symbol, and the data field includes the third symbol,

wherein the frame further includes a first HE signal field and a second HE signal field that both follow the legacy preamble part,

wherein a basic bandwidth of the frame is divided into a plurality of subbands, and the data field is encoded per a subband unit and transmitted on a subband of the plurality of subbands,

wherein the second HE signal field is encoded per the basic bandwidth and transmitted, and includes allocation information for the subbands,

wherein the data field transmitted on a first subband includes data for a first receiving device allocated to the subband,

wherein the frame includes a guard band between the first subband and a second subband when the second subband is allocated to a second receiving device, and

wherein the frame does not include the guard band between the first subband and the second subband when the second subband is allocated to the first receiving device,

wherein the second subband is adjacent to the first subband.

10. The method of claim 9 , wherein processing the first symbol and the second symbol includes:

performing a Fourier transform on the first symbol by using a fast Fourier transform (FFT) having a first size; and

performing a Fourier transform on the second symbol by using an FFT having a second size different from the first size.

11. The method of claim 10 , wherein the second size is four times the first size, and

wherein performing the Fourier transform on the second symbol includes:

generating an interval having two periods by copying an interval excluding a guard interval from the second symbol; and

performing the Fourier transform on the interval having the two periods.

12. The method of claim 9 , wherein the first length is 3.2 μs and the second length is 6.4 μs.

13. The method of claim 9 , wherein the second HE signal field further includes information on devices that receive the frame on each subband.

14. The method of claim 9 , wherein the legacy preamble part further includes a legacy signal field, and

wherein two symbols that immediately follow the legacy signal field are modulated by using BPSK (binary phase shift keying) modulation.