Method and apparatus for configuring long training field in wireless local network system

1. A method of performing communications in a wireless LAN system, the method comprising:

configuring, by a transmitting apparatus, a second Long training Field (LTF) sequence of a second wireless LAN system by re-using a first LTF sequence of a first wireless LAN system to minimize a full band peak-to-average power ratio (PAPR); and

transmitting, by the transmitting apparatus, the second LTF sequence via a Physical layer Protocol Data Unit (PPDU) including a first field region and a second field region,

wherein the second LTF sequence includes first tones indicated by first tone indices obtained by up-scaling tone indices of the first LTF sequence by four times and second tones in which coefficients are inserted into null tones generated by up-scaling the tone indices of the first LTF sequence by four times,

wherein a phase rotation is applied to the first LTF sequence for each 20 MHz before the tone indices of the first LTF sequence is up-scaled by four times,

wherein if the second LTF sequence is transmitted via 20 MHz, the second LTF sequence is defined as follow,

HELTF(−120:4:120)={1,1,1,1,LTF left,0,LTF right,−1,−1,−1,1},

wherein if the second LTF sequence is transmitted via 40 MHz, the second LTF sequence is defined as follow,

HELTF(−244:4:244)={−1,−1,1,LTF left,1,LTF right,−1,−1,−1,1,−1,0,−1,−1,1,1,−1,LTF left,1,LTF right,1,1,1}, or HELTF(−244:4:244)={1,1,−1,−LTF left,−1,−LTF right,1,1,1,−1,1,0,1,1,−1,−1,1,−LTF left,−1,−LTF right,−1,−1,−1}(see Moon slide 167 Option 1),

wherein if the second LTF sequence is transmitted via 80 MHz, the second LTF sequence is defined as follow,

HELTF_(−500:4:500)={−1,−1,1,LTF left,1,LTF right,−1,−1,−1,1,1,−1,1,−1,1,1,−1,LTF left,1,LTF right,1,−1,1,−1,1,0,1,1,−1,−1,1,LTF left,1,LTF right,−1,−1,−1,1,1,1,−1,1,−1,−1,1,−LTF left,−1,−LTF right,−1,−1,−1} or HELTF(−500:4:500)={1,1,−1,−LTF left,−1,−LTF right,1,1,1,−1,−1,1,−1,1,−1,−1,1,−LTF left,−1,−LTF right,−1,1,−1,1,−1,0,−1,−1,1,1,−1,−LTF left,−1,−LTF right,1,1,1,−1,−1,−1,1,−1,1,1,−1,LTF left,1,LTF right,1,1,1}(see Moon slide 169),

wherein the LTF left is defined as follow,

LTF left={1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,1,1,−1,−1,1,1,−1,1,−1,1,1,1,1}(see Moon slide 38), and

wherein the LTF right is defined as follow,

LTF_right={1,−1,−1,1,1,−1,1,−1,1,−1,−1,−1,−1,−1,1,1,−1,−1,1,−1,1,−1,1,1,1,1}.

2. The method of claim 1 ,

wherein when the first LTF sequence is configured to be transmitted for a first frequency band, the second LTF sequence is transmitted via the first frequency band, and

wherein a bandwidth of the first frequency band is 20 MHz, 40 MHz, or 80 MHz.

3. The method of claim 1 ,

wherein the first LTF sequence is a Very High Throughput (VHT) LTF sequence, and the second LTF sequence of is a High Efficiency (HE) LTF, and

wherein the PPDU is HE PPDU.

4. The method of claim 1 ,

wherein an Inverse Discrete Fourier Transform (IDFT)/Discrete Fourier Transform (DFT) period applied to each symbol of the first field region has the same length as an IDFT/DFT period applied to each symbol of the second field region.

5. A transmitting apparatus of performing communications in a wireless LAN system,

a radio frequency (RF) unit that transmits and receives a wireless signal; and

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

configure a second Long training Field (LTF) sequence of a second wireless LAN system by re-using a first LTF sequence of a first wireless LAN system to minimize a full band peak-to-average power ratio (PAPR); and

transmit the second LTF sequence of the second wireless LAN system via a Physical layer Protocol Data Unit (PPDU) PPDU (Physical layer Protocol Data Unit) including a first field region and a second field region,

wherein the second LTF sequence includes first tones indicated by first tone indices obtained by up-scaling tone indices of the first LTF sequence by four times and second tones in which coefficients are inserted into null tones generated by up-scaling the tone indices of the first LTF sequence by four times,

wherein a phase rotation is applied to the first LTF sequence for each 20 MHz before the tone indices of the first LTF sequence is up-scaled by four times,

wherein if the second LTF sequence is transmitted via 20 MHz, the second LTF sequence is defined as follow,

HELTF(−120:4:120)={1,1,1,1,LTF left,0,LTF right,−1,−1,−1,1}).

wherein if the second LTF sequence is transmitted via 40 MHz, the second LTF sequence is defined as follow,

HELTF(−244:4:244)={−1,−1,1,LTF left,1,LTF right,−1,−1,−1,1,−1,0,−1,−1,1,1,−1,LTF left,1,LTF right,1,1,1}, or HELTF(−244:4:244)={1,1,−1,−LTF left,−1,−LTF right,1,1,1,−1,1,0,1,1,−1,−1,1,−LTF left,−1,−LTF right,−1,−1,−1}(see Moon slide 167 Option 1),

wherein if the second LTF sequence is transmitted via 80 MHz, the second LTF sequence is defined as follow,

HELTF_(−500:4:500)={−1,−1,1,LTF left,1,LTF right,−1,−1,−1,1,1,−1,1,−1,1,1,−1,LTF left,1,LTF right,1,−1,1,−1,1,0,1,1,−1,−1,1,LTF left,1,LTF right,−1,−1,−1,1,1,1,−1,1,−1,−1,1,−LTF left,−1,−LTF right,−1,−1,−1} or HELTF(−500:4:500)={1,1,−1,−LTF left,−1,−LTF right,1,1,1,−1,−1,1,−1,1,−1,−1,1,−LTF left,−1,−LTF right,−1,1,−1,1,−1,0,−1,−1,1,1,−1,−LTF left,−1,−LTF right,1,1,1,−1,−1,−1,1,−1,1,1,−1,LTF left,1,LTF right,1,1,1}(see Moon slide 169),

wherein the LTF left is defined as follow,

LTF left={1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,1,1,−1,−1,1,1,−1,1,−1,1,1,1,1}(see Moon slide 38), and

wherein the LTF right is defined as follow,

LTF_right={1,−1,−1,1,1,−1,1,−1,1,−1,−1,−1,−1,−1,1,1,−1,−1,1,−1,1,−1,1,1,1,1}.

6. The transmitting apparatus of claim 5 ,

wherein when the first LTF sequence is configured to be transmitted for a first frequency band, the second LTF sequence is transmitted via the first frequency band, and

wherein a bandwidth of the first frequency band is 20 MHz, 40 MHz, or 80 MHz.

7. The transmitting apparatus of claim 5 ,

wherein the first LTF sequence is a Very High Throughput (VHT) LTF sequence, and the second LTF sequence is a High Efficiency (HE) LTF, and

wherein the PPDU is HE PPDU.

8. The transmitting apparatus of claim 5 , wherein an Inverse Discrete Fourier Transform (IDFT)/Discrete Fourier Transform (DFT) period applied to each symbol of the first field region has the same length as an IDFT/DFT period applied to each symbol of the second field region.

9. The method of claim 1 ,

wherein the HELTF (−120:4:120) means that tones are inserted, with ranging tone indices from −120 to 120, with the spacing of tone index of 4,

wherein the HELTF (−244:4:244) means that tones are inserted, with ranging tone indices from −244 to 244, with the spacing of tone index of 4, and

wherein the HELTF_(−500:4:500) means that tones are inserted, with ranging tone indices from −500 to 500, with the spacing of tone index of 4.

10. The transmitting apparatus of claim 5 ,

wherein the HELTF (−120:4:120) means that tones are inserted, with ranging tone indices from −120 to 120, with the spacing of tone index of 4,

wherein the HELTF (−244:4:244) means that tones are inserted, with ranging tone indices from −244 to 244, with the spacing of tone index of 4, and

wherein the HELTF (−500:4:500) means that tones are inserted, with ranging tone indices from −500 to 500, with the spacing of tone index of 4.