Preamble formats for MIMO wireless communications

1. A method for generating a preamble of a frame for a multiple input multiple output (MIMO) wireless communication, the method comprises:

for each transmit antenna of the MIMO wireless communication, generating a carrier detect field, wherein, from transmit antenna to transmit antenna, the carrier detect field is cyclically shifted;

for a first grouping of the transmit antennas of the MIMO wireless communication:

generating a first guard interval following the carrier detect field; and

generating at least one channel sounding field, wherein, from transmit antenna to transmit antenna in the first grouping, the at least one channel sounding field is cyclically shifted, and wherein the at least one channel sounding field follows the first guard interval; and

when the MIMO wireless communication includes more than the first grouping of the transmit antennas, for another grouping of the transmit antennas:

generating at least one other channel sounding field, wherein, from transmit antenna to transmit antenna in the another grouping, the at least one other channel sounding field is cyclically shifted, and wherein the at least one other channel sounding field follows the at least one channel sounding field; and

generating the first guard interval prior to the at least one other channel sounding field.

2. The method of claim 1 further comprises, for each antenna of the first grouping of the transmit antennas of the MIMO wireless communication:

generating a second guard interval following the at least one channel sounding field; and

generating a signal field following the second guard interval.

3. The method of claim 2 further comprises, for each antenna of the another grouping of the transmit antennas:

generating a third guard interval preceding the at least one other channel sounding, wherein the first and third guard intervals are greater in duration than the second guard interval.

4. The method of claim 1 , wherein the generating the carrier detect field comprises:

generating a short training sequence in accordance with a legacy protocol, wherein the cyclic shift to the carrier detect field is either of a forward or a backward direction and is based on a number of the transmit antennas and duration of the short training sequence.

5. The method of claim 4 further comprises, when the number of transmit antennas is three:

for the first grouping of the transmit antennas of the MIMO wireless communication, generating a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the three transmit antennas, wherein the first and second long training sequences are respectively cyclically shifted; and

generating a third long training sequence in accordance with the legacy protocol as the at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes a third of the three transmit antennas.

6. The method of claim 4 further comprises, when the number of transmit antennas is four:

for the first grouping of the transmit antennas of the MIMO wireless communication, generating a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the four transmit antennas, wherein the first and second long training sequences are respectively cyclically shifted; and

generating third and fourth long training sequences in accordance with the legacy protocol as at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes another two of the four transmit antennas, wherein the third and fourth long training sequences are respectively cyclically shifted.

7. The method of claim 1 further comprises for each of the transmit antennas of the MIMO wireless communication:

generating another guard interval following the at least one other channel sounding field; and

generating a second signal field following the another guard interval.

8. A method for generating a legacy compatible preamble of a frame for a multiple input multiple output (MIMO) wireless communication, the method comprises:

for each transmit antenna of a plurality of transmit antennas for the MIMO wireless communication, generating a carrier detect field, wherein, from transmit antenna to transmit antenna, the carrier detect field is cyclically shifted;

for a first transmit antenna of the plurality of transmit antennas:

generating a first guard interval following the carrier detect field;

generating a first channel sounding field following the first guard interval;

generating a second channel sounding field following the first channel sounding field;

for each transmit antenna of a first grouping of remaining transmit antennas of the plurality of transmit antennas:

generating a third channel sounding field;

generating a fourth channel sounding field following the third channel sounding field; and

generating a second guard interval preceding the third channel sounding field.

9. The method of claim 8 , wherein when the plurality of transmit antennas includes three transmit antennas:

from transmit antenna to transmit antenna in the first grouping, cyclically shifting the third and fourth channel sounding fields respectively.

10. The method of claim 9 , wherein when the plurality of transmit antennas includes four transmit antennas:

for a fourth transmit antenna of the plurality of transmit antennas:

generating a fifth channel sounding field;

generating a sixth channel sounding field following the fifth channel sounding field; and

generating a third guard interval preceding the fifth channel sounding field.

11. The method of claim 10 further comprises for each of the plurality of transmit antennas:

generating another guard interval following the sixth channel sounding field; and

generating a signal field following the second guard interval.

12. The method of claim 8 further comprises, for the first transmit antenna:

generating another guard interval following the second channel sounding field; and

generating a signal field following the second guard interval.

13. The method of claim 8 , wherein the generating the carrier detect field comprises:

generating a short training sequence in accordance with a legacy protocol, wherein the cyclic shift to the carrier detect field is either of a forward or a backward direction and is based on a number of the transmit antennas and duration of the short training sequence.

14. The method of claim 8 further comprises for each of the transmit antennas of the MIMO wireless communication:

generating another guard interval following the fourth channel sounding field; and

generating a second signal field following the another guard interval.

15. A radio frequency (RF) transmitter comprises:

a baseband processing module that produces outbound symbol streams from outbound data; and

a transmitter section that produces outbound RF signals from the outbound symbol streams, wherein the baseband processing module is operable to:

for each transmit antenna of the transmitter section, generate a carrier detect field, wherein, from transmit antenna to transmit antenna, the carrier detect field is cyclically shifted;

for a first grouping of the transmit antennas of the transmitter section:

generate a first guard interval following the carrier detect field; and

generate at least one channel sounding field, wherein, from transmit antenna to transmit antenna in the first grouping, the at least one channel sounding field is cyclically shifted, and wherein the at least one channel sounding field follows the first guard interval; and

when the transmitter section includes more than the first grouping of the transmit antennas, for another grouping of the transmit antennas:

generate at least one other channel sounding field, wherein, from transmit antenna to transmit antenna in the another grouping, the at least one other channel sounding field is cyclically shifted, and wherein the at least one other channel sounding field follows the at least one channel sounding field; and

generate the first guard interval prior to the at least one other channel sounding field.

16. The RF transmitter of claim 15 , wherein the baseband processing module is further operable to, for each antenna of the first grouping of the transmit antennas of the transmitter section:

generate a second guard interval following the at least one channel sounding field; and

generate a signal field following the second guard interval.

17. The RF transmitter of claim 16 , wherein the baseband processing module is further operable to, for each antenna of the another grouping of the transmit antennas:

generate a third guard interval preceding the at least one other channel sounding, wherein the first and third guard intervals are greater in duration than the second guard interval.

18. The RF transmitter of claim 15 , wherein the baseband processing module is further operable to generate the carrier detect field by:

generating a short training sequence in accordance with a legacy protocol, wherein the cyclic shift to the carrier detect field is either of a forward or a backward direction and is based on a number of the transmit antennas and duration of the short training sequence.

19. The RF transmitter of claim 18 , wherein the baseband processing module is further operable to, when the number of transmit antennas is three:

for the first grouping of the transmit antennas of the transmitter section, generate a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the three transmit antennas, wherein the first and second long training sequences are respectively cyclically shifted; and

generate a third long training sequence in accordance with the legacy protocol as the at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes a third of the three transmit antennas.

20. The RF transmitter of claim 18 , wherein the baseband processing module is further operable to, when the number of transmit antennas is four:

for the first grouping of the transmit antennas of the transmitter section, generate a first and second long training sequence in accordance with the legacy protocol as at least one channel sounding field, wherein the first grouping includes two of the four transmit antennas, wherein the first and second long training sequences are respectively cyclically shifted; and

generate third and fourth long training sequences in accordance with the legacy protocol as at least one other channel sounding field for the another grouping of the transmit antennas, wherein the another grouping includes another two of the four transmit antennas, wherein the third and fourth long training sequences are respectively cyclically shifted.