Extended guard interval for outdoor WLAN

1. A method for generating a physical layer (PHY) data unit for transmission via a wireless communication channel, the method comprising:

selecting, at a wireless network interface device, a guard interval from a set of different guard intervals including a first guard interval, a second guard interval, and a third guard interval, wherein a first wireless communication protocol supports the set of different guard intervals, and wherein a legacy second communication protocol supports the first guard interval but does not support at least the third guard interval;

generating, at the wireless network interface device, the PHY data unit, wherein the PHY data unit is generated to conform to the first wireless communication protocol, wherein generating the PHY data unit includes generating a PHY preamble and a PHY data portion, and wherein:

the PHY preamble includes a legacy portion having a legacy first signal field, a first non-legacy portion having a second signal field, and a second non-legacy portion having a third signal field,

the second signal field in the first non-legacy portion includes a multi-bit subfield that indicates the selected guard interval for the second non-legacy portion of the PHY preamble and the PHY data portion of the PHY data unit,

the legacy first signal field and the first non-legacy portion of the PHY preamble are generated using the first guard interval, and

the second non-legacy portion of the PHY preamble and the PHY data portion are generated using the selected guard interval indicated by the multi-bit subfield in the first non-legacy portion of the PHY preamble.

2. The method of claim 1 , wherein the multi-bit subfield in the first non-legacy portion of the PHY preamble that indicates the selected guard interval consists of two bits.

3. The method of claim 1 , wherein the first guard interval is 0.8 μs.

4. The method of claim 3 , wherein one of the guard intervals in the set of different guard intervals other than the first guard interval is 1.6 μs.

5. The method of claim 3 , wherein one of the guard intervals in the set of different guard intervals other than the first guard interval is 1.2 μs.

6. The method of claim 3 , wherein one of the guard intervals in the set of different guard intervals other than the first guard interval is 0.4 μs.

7. The method of claim 1 , wherein the legacy portion includes a first training field generated using the first guard interval, and the second non-legacy portion includes a second training field generated using the selected guard interval.

8. The method of claim 1 , further comprising:

transmitting, by the wireless network interface device, the PHY data unit via one or more antennas.

9. An apparatus comprising:

a wireless network interface device having one or more integrated circuit (IC) devices configured to:

select a guard interval from a set of different guard intervals including a first guard interval, a second guard interval, and a third guard interval, wherein a first wireless communication protocol supports the set of different guard intervals, and wherein a legacy second communication protocol supports the first guard interval but does not support at least the third guard interval,

generate a physical layer (PHY) data unit, wherein the PHY data unit is generated to conform to the first wireless communication protocol, wherein generating the PHY data unit includes generating a PHY preamble and a PHY data portion, and wherein:

the PHY preamble includes a legacy portion having a legacy first signal field, a first non-legacy portion having a second signal field, and a second non-legacy portion having a third signal field,

the second signal field in the first non-legacy portion includes a multi-bit subfield that indicates the selected guard interval for the second non-legacy portion of the PHY preamble and the PHY data portion of the PHY data unit,

the legacy first signal field and the first non-legacy portion of the PHY preamble are generated using the first guard interval, and

the second non-legacy portion of the PHY preamble and the PHY data portion are generated using the selected guard interval indicated by the multi-bit subfield in the first non-legacy portion of the PHY preamble.

10. The apparatus of claim 9 , wherein the multi-bit subfield in the first non-legacy portion of the PHY preamble that indicates the selected guard interval consists of two bits.

11. The apparatus of claim 9 , wherein the first guard interval is 0.8 μs.

12. The apparatus of claim 11 , wherein one of the guard intervals in the set of different guard intervals other than the first guard interval is 1.6 μs.

13. The apparatus of claim 11 , wherein one of the guard intervals in the set of different guard intervals other than the first guard interval is 1.2 μs.

14. The apparatus of claim 11 , wherein one of the guard intervals in the set of different guard intervals other than the first guard interval is 0.4 μs.

15. The apparatus of claim 9 , wherein the legacy portion includes a first training field generated using the first guard interval, and the second non-legacy portion includes a second training field generated using the selected guard interval.

16. The apparatus of claim 9 , wherein the one or more IC devices are further configured to:

transmit the PHY data unit via one or more antennas.

17. The apparatus of claim 9 , wherein the wireless network interface device comprises:

a physical layer (PHY) processing unit implemented on the apparatus;

wherein the PHY processing unit is configured to generate the PHY data unit.

18. The apparatus of claim 17 , wherein the PHY processing unit comprises:

one or more transceivers implemented on the one or more IC devices.

19. The apparatus of claim 18 , further comprising:

one or more antennas coupled to the one or more transceivers.