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:

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

generating a first guard interval, at least one channel sounding field with respect to each transmit antenna of the first grouping, and at least one channel sounding field; and

for each transmit antenna of the first grouping, applying a cyclic shift to the at least one channel sounding field prior to transmission; 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 for each transmit antenna of the another grouping; and

for each transmit antenna of the another grouping, applying another cyclic shift to the at least one other channel sounding field prior to transmission of the another grouping.

2. The method of claim 1 further comprises, for each transmit 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 transmit antenna of the another grouping of the transmit antennas:

generating a third guard interval preceding the at least one other channel sounding field, wherein the first and third guard intervals are greater in a 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 is based on a number of the transmit antennas and a 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; 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; 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.

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 such that the another guard interval is not adjacent to the first guard interval; 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:

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

generating a first guard interval, a first channel sounding field following the first guard interval, and a second channel sounding field; and

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

generating a third channel sounding field, a fourth channel sounding field, and a second guard interval; and

applying a cyclic shift to the carrier detect field prior to transmission via the each transmit antenna of the first antenna and of the first grouping of the remaining transmit antennas.

9. The method of claim 8 , 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, a sixth channel sounding field, and a third guard interval preceding the fifth channel sounding field.

10. The method of claim 9 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.

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

generating another guard interval following the second channel sounding field such that the another guard interval is not adjacent the first guard interval; and

generating a signal field following the second guard interval.

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

generating a short training sequence in accordance with a legacy protocol is based on a number of the transmit antennas and a duration of the short training sequence.

13. 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.

14. A radio frequency (RF) transmitter comprises:

a baseband processing module configured to produce outbound symbol streams from outbound data; and

a transmitter section configured to produce outbound RF signals from the outbound symbol streams, wherein the baseband processing module configured to:

for each transmit antenna of the transmitter section, generate a carrier detect field:

generate a first guard interval, at least one channel sounding field; and

for each transmit antenna of the first grouping, applying a cyclic shift to the carrier detect field prior to transmission; 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 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; and

for each transmit antenna of the another grouping, applying another cyclic shift to the carrier detect field prior to transmission of the another grouping.

15. The RF transmitter of claim 14 , 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 such that the second guard interval is not adjacent the first guard interval; and

generate a signal field following the second guard interval.

16. The RF transmitter of claim 15 , 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 a duration than the second guard interval.

17. The RF transmitter of claim 14 , 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 based on a number of the transmit antennas and a duration of the short training sequence.

18. The RF transmitter of claim 17 , 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; 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.

19. The RF transmitter of claim 17 , 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; 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.

20. The RF transmitter of claim 14 , wherein an amount of the cyclic shift per antenna is based upon a total number of the transmit antennas.