Method and apparatus of transmitting training signal in wireless local area network system

1. A method of transmitting a training signal in a Wireless Local Area Network (WLAN) system, the method comprising:

generating, by a transmitting station, Very High Throughput-Long Training Field (VHT-LTF) symbols used for at least one receiving station, the VHT-LTF symbols generated by applying a mapping matrix P to a VHT-LTF sequence,

wherein the mapping matrix P is set to a first mapping matrix P when a total number of spatial streams for the at least one receiving station is set to seven (7),

wherein the mapping matrix P is set to the first mapping matrix P when the total number of spatial streams for the at least one receiving station is set to eight (8),

wherein the mapping matrix P is set to a second mapping matrix P when the total number of spatial streams for the at least one receiving station is set to five (5),

wherein the mapping matrix P is set to the second mapping matrix P when the total number of spatial streams for the at least one receiving station is set to six (6),

wherein the mapping matrix P is set to a third mapping matrix P when the total number of spatial streams for the at least one receiving station is set to three (3),

wherein the mapping matrix P is set to the third mapping matrix P when the total number of spatial streams for the at least one receiving station is set to four (4), and

wherein a number of the VHT-LTF symbols is set to eight (8) when the total number of spatial streams for the at least one receiving station is set to seven (7); and

transmitting, by the transmitting station, the VHT-LTF symbols to the at least one receiving station,

wherein the third mapping matrix P is a 4-by-4 submatrix, which is denoted by P 1 ,

wherein the first mapping matrix P is an 8-by-8 matrix configured in a form of

[

⁢

P

1

P

1

P

1

-

P

1

⁢

]

wherein the second mapping matrix P is a 6-by-6 matrix configured in a form of

[

P

2

P

3

P

4

P

5

]

,

wherein a first seven rows of the first mapping matrix P are applied when the total number of spatial streams for the at least one receiving station is set to seven (7),

wherein a first five rows of the second mapping matrix P are applied when the total number of spatial streams for the at least one receiving station is set to five (5), and

wherein the second mapping matrix P is configured in the form of

[

P

2

P

3

P

4

P

5

]

,

and P 2 to P 5 are four different 3-by-3 submatrices.

2. The method of claim 1 , wherein a number of the VHT-LTF symbols is set to six (6) when the total number of spatial streams for the at least one receiving station is set to five (5).

3. The method of claim 1 , wherein the plurality of VHT-LTF symbols are used to estimate a multiple input multiple output (MIMO) channel of a wireless channel of the at least one receiving station.

4. The method of claim 1 , wherein P 1 is determined by

[

1

-

1

1

1

1

1

-

1

1

1

1

1

-

1

-

1

1

1

1

]

.

5. A transmitting station, comprising:

a processor configured to generate Very High Throughput-Long Training Field (VHT-LTF) symbols used for at least one receiving station, the VHT-LTF symbols generated by applying a mapping matrix P to a VHT-LTF sequence,

wherein the mapping matrix P is set to a first mapping matrix P when a total number of spatial streams for the at least one receiving station is set to seven (7),

wherein the mapping matrix P is set to the first mapping matrix P when the total number of spatial streams for the at least one receiving station is set to eight (8),

wherein the mapping matrix P is set to a second mapping matrix P when the total number of spatial streams for the at least one receiving station is set to five (5),

wherein the mapping matrix P is set to the second mapping matrix P when the total number of spatial streams for the at least one receiving station is set to six (6),

wherein the mapping matrix P is set to a third mapping matrix P when the total number of spatial streams for the at least one receiving station is set to three (3),

wherein the mapping matrix P is set to the third mapping matrix P when the total number of spatial streams for the at least one receiving station is set to four (4), and

wherein a number of the VHT-LTF symbols is set to eight (8) when the total number of spatial streams for the at least one receiving station is set to seven (7); and

a transmitter configured to transmit the VHT-LTF symbols to the at least one receiving station,

wherein the third mapping matrix P is a 4-by-4 submatrix, which is denoted by P 1 ,

wherein the first mapping matrix P is an 8-by-8 matrix configured in a form of

[

P

1

P

1

P

1

-

P

1

]

wherein the second mapping matrix P is a 6-by-6 matrix configured in a form of

[

P

2

P

3

P

4

P

5

]

,

wherein a first seven rows of the first mapping matrix P are applied when the total number of spatial streams for the at least one receiving station is set to seven (7),

wherein a first five rows of the second mapping matrix P are applied when the total number of spatial streams for the at least one receiving station is set to five (5), and

wherein the second mapping matrix P is configured in a form of and

[

P

2

P

3

P

4

P

5

]

,

P 2 to P 5 are four different 3-by-3 submatrices.

6. The transmitting station of claim 5 , wherein a number of the VHT-LTF symbols is set to six (6) when the total number of spatial streams for the at least one receiving station is set to five (5).

7. The transmitting station of claim 5 , wherein the plurality of VHT-LTF symbols are used to estimate a multiple input multiple output (MIMO) channel of a wireless channel of the at least one receiving station.

8. The transmitting station of claim 5 , wherein P 1 is determined by

[

1

-

1

1

1

1

1

-

1

1

1

1

1

-

1

-

1

1

1

1

]

.