Apparatus and method for diversity transmission in a wireless communications system

1. A transmission apparatus comprising:

a transmission signal generator which, in operation, generates a transmission signal that includes a non-legacy preamble and a data field, the non-legacy preamble comprising a first field for indicating a number of spatial streams (Nss) in the data field and a second field for indicating one of a plurality of modulation and coding schemes (MCSs), wherein two or more frequency diversity transmission schemes are supported and one of the two or more frequency diversity transmission schemes is specified based on a value of the Nss; and

a transmitter which, in operation, transmits the generated transmission signal.

2. The transmission apparatus according to claim 1 , wherein the non-legacy preamble comprises a third field for indicating whether at least one of the two or more frequency diversity transmission schemes is applied to the data field.

3. The transmission apparatus according to claim 1 , wherein the two or more frequency diversity transmission schemes include a first scheme which is a frequency diversity scheme without spatial diversity.

4. The transmission apparatus according to claim 3 , wherein if the value of the Nss equals to a first determined value and the non-legacy preamble indicates that the first scheme is applied to the data field, the first scheme is applied to at least one of the spatial streams.

5. The transmission apparatus according to claim 4 , wherein the first determined value is an odd number.

6. The transmission apparatus according to claim 3 , wherein the two or more frequency diversity transmission schemes include a second scheme which is a space-frequency diversity scheme (SFDS).

7. The transmission apparatus according to claim 6 , wherein the first scheme and the second scheme are applied if the value of the Nss is an odd value.

8. The transmission apparatus according to claim 7 , wherein more than two spatial streams are paired into Np=floor (Nss/2) spatial stream pairs and one of spatial streams is unpaired if the value of the Nss is larger than 3.

9. The transmission apparatus according to claim 8 , wherein the first scheme is applied to the unpaired spatial stream and the second scheme is applied to each of the Np spatial stream pairs.

10. The transmission apparatus according to claim 8 , wherein the spatial streams can be paired based on physical antenna configuration and mapping of spatial streams to antennas.

11. The transmission apparatus according to claim 6 , wherein the second scheme is applied to the data field if the value of the Nss is an even value.

12. The transmission apparatus according to claim 1 , wherein the spatial streams are grouped into Ng=floor (Nss/2) spatial stream groups if the value of the Nss is an odd value, wherein one of the Ng groups comprises three spatial streams and each of the remaining (Ng−1) groups comprises two spatial streams.

13. The transmission apparatus according to claim 12 , wherein an enhanced Space Frequency Diversity Scheme (e-SFDS) is applied to a three-spatial-stream group and a SFDS is applied to each of the remaining (Ng−1) two-spatial-stream groups.

14. The transmission apparatus according to claim 12 , wherein the spatial streams can be grouped based on physical antenna configuration and mapping of the spatial streams to antennas.

15. A transmission apparatus comprising:

a transmission signal generator which, in operation, generates a transmission signal that includes a non-legacy preamble and a data field, the non-legacy preamble comprising a first field for indicating a number of spatial streams (Nss) in the data field and a second field for indicating one of a plurality of modulation and coding schemes (MCSs), wherein two or more frequency diversity transmission schemes are supported; and

a transmitter which, in operation, transmits the generated transmission signal, wherein

a first scheme of the two or more frequency diversity transmission schemes is a frequency diversity scheme without spatial diversity and

a second scheme of the two or more frequency diversity transmission schemes is a space-frequency diversity scheme, and

the first scheme is applied to at least one spatial stream if the non-legacy preamble indicates that at least one of the two or more frequency diversity transmission schemes is applied to the data field and the value of the Nss is an odd number.

16. A transmission method comprising:

generating a transmission signal that includes a non-legacy preamble and a data field, the non-legacy preamble comprising a first field for indicating a number of spatial streams (Nss) in the data field and a second field for indicating one of a plurality of modulation and coding schemes (MCSs), wherein two or more frequency diversity transmission schemes are supported and one of the two or more frequency diversity transmission schemes is specified based on a value of the Nss; and

transmitting the generated transmission signal.