Generating packets having orthogonal frequency division multiplexing (OFDM) symbols

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

generating, at a communication device, a first portion of a PHY preamble of the PHY data unit to include a first plurality of orthogonal frequency division multiplexing (OFDM) symbols, wherein each OFDM symbol of the first plurality of OFDM symbols is generated with a first OFDM tone spacing;

generating, at the communication device, a second portion of the PHY preamble to include a second plurality of OFDM symbols, wherein each OFDM symbol of the second plurality of OFDM symbols is generated with a second OFDM tone spacing, wherein

the second OFDM tone spacing is a fraction 1/N of the first OFDM tone spacing, and

N is a positive integer greater than one;

generating, at the communication device, a PHY data portion of the PHY data unit to include one or more third OFDM symbols, wherein each third OFDM symbol is generated with the second OFDM tone spacing; and

transmit, by the communication device, the PHY data unit via the communication channel.

2. The method of claim 1 , wherein:

generating the first portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the first plurality of OFDM symbols to have a first duration;

generating the second portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the second plurality of OFDM symbols to have a second duration that is at least double the first duration; and

generating the PHY data portion includes generating the third OFDM symbols to have a third duration that is at least double the first duration.

3. The method of claim 2 , wherein:

the first portion of the PHY preamble includes a PHY signal field; and

the second portion of the PHY preamble includes one or more training fields.

4. The method of claim 1 , wherein:

generating the first portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the first plurality of OFDM symbols to span 20 MHz and include at most 64 OFDM subcarriers;

generating the second portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the second plurality of OFDM symbols to span 20 MHz and include N*64 OFDM subcarriers; and

generating the PHY data portion includes generating the third OFDM symbols to span 20 MHz and include N*64 OFDM subcarriers.

5. The method of claim 1 , wherein:

generating the first portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the first plurality of OFDM symbols to span 40 MHz and include at most 128 OFDM subcarriers;

generating the second portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the second plurality of OFDM symbols to span 40 MHz and include N*128 OFDM subcarriers; and

generating the PHY data portion includes generating the third OFDM symbols to span 40 MHz and include N*128 OFDM subcarriers.

6. The method of claim 1 , wherein:

generating the first portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the first plurality of OFDM symbols to span 80 MHz and include at most 256 OFDM subcarriers;

generating the second portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the second plurality of OFDM symbols to span 80 MHz and include N*256 OFDM subcarriers; and

generating the PHY data portion includes generating the third OFDM symbols to span 80 MHz and include N*256 OFDM subcarriers.

7. The method of claim 1 , wherein:

generating the first portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the first plurality of OFDM symbols to span 160 MHz cumulatively and include at most 512 OFDM subcarriers;

generating the second portion of the PHY preamble of the PHY data unit includes generating OFDM symbols among the second plurality of OFDM symbols to span 160 MHz cumulatively and include N*512 OFDM subcarriers; and

generating the PHY data portion includes generating the third OFDM symbols to span 160 MHz cumulatively and include N*512 OFDM subcarriers.

8. The method of claim 7 , wherein:

generating the second portion of the PHY preamble of the PHY data unit includes:

i) generating a first 80 MHz segment using a first N*256-point inverse discrete Fourier transform (IDFT) calculator, and ii) generating a second 80 MHz segment using a second N*256-point IDFT calculator; and

generating the PHY data portion includes: i) generating a first 80 MHz segment using the first N*256-point IDFT calculator, and ii) generating a second 80 MHz segment using the second N*256-point IDFT calculator.

9. The method of claim 1 , wherein N is four.

10. The method of claim 9 , wherein:

the first OFDM tone spacing is 312.5 kHz; and

the second OFDM tone spacing is 78.125 kHz.

11. An apparatus, comprising:

a network interface device having one or more integrated circuits (ICs) configured to:

generate a first portion of a PHY preamble of a PHY data unit to include a first plurality of orthogonal frequency division multiplexing (OFDM) symbols, wherein each OFDM symbol of the first plurality of OFDM symbols is generated with a first OFDM tone spacing,

generate a second portion of the PHY preamble to include a second plurality of OFDM symbols, wherein each OFDM symbol of the second plurality of OFDM symbols is generated with a second OFDM tone spacing, wherein

the second OFDM tone spacing is a fraction 1/N of the first OFDM tone spacing, and

N is a positive integer greater than one; and

wherein the one or more ICs are further configured to:

generate a PHY data portion of the PHY data unit to include one or more third OFDM symbols, wherein each third OFDM symbol is generated with the second OFDM tone spacing, and

transmit the PHY data unit via a communication channel.

12. The apparatus of claim 11 , wherein the one or more ICs are further configured to:

generate OFDM symbols among the first plurality of OFDM symbols to have a first duration;

generate OFDM symbols among the second plurality of OFDM symbols to have a second duration that is at least double the first duration; and

generate the third OFDM symbols to have a third duration that is at least double the first duration.

13. The apparatus of claim 12 , wherein:

the first portion of the PHY preamble includes a PHY signal field; and

the second portion of the PHY preamble includes one or more training fields.

14. The apparatus of claim 11 , wherein the one or more ICs are further configured to:

generate OFDM symbols among the first plurality of OFDM symbols to span 20 MHz and include at most 64 OFDM subcarriers;

generate OFDM symbols among the second plurality of OFDM symbols to span 20 MHz and include N*64 OFDM subcarriers; and

generate the third OFDM symbols to span 20 MHz and include N*64 OFDM subcarriers.

15. The apparatus of claim 11 , wherein the one or more ICs are further configured to:

generate OFDM symbols among the first plurality of OFDM symbols to span 40 MHz and include at most 128 OFDM subcarriers;

generate OFDM symbols among the second plurality of OFDM symbols to span 40 MHz and include N*128 OFDM subcarriers; and

generate the third OFDM symbols to span 40 MHz and include N*128 OFDM subcarriers.

16. The apparatus of claim 11 , wherein the one or more ICs are further configured to:

generate OFDM symbols among the first plurality of OFDM symbols to span 80 MHz and include at most 256 OFDM subcarriers;

generate OFDM symbols among the second plurality of OFDM symbols to span 80 MHz and include N*256 OFDM subcarriers; and

generate the third OFDM symbols to span 80 MHz and include N*256 OFDM subcarriers.

17. The apparatus of claim 11 , wherein the one or more ICs are further configured to:

generate OFDM symbols among the first plurality of OFDM symbols to span 160 MHz cumulatively and include at most 512 OFDM subcarriers;

generate OFDM symbols among the second plurality of OFDM symbols to span 160 MHz cumulatively and include N*512 OFDM subcarriers; and

generate the third OFDM symbols to span 160 MHz cumulatively and include N*512 OFDM subcarriers.

18. The apparatus of claim 17 , further comprising:

a first N*256-point inverse discrete Fourier transform (IDFT) calculator implemented on the one or more ICs; and

a second N*256-point IDFT calculator implemented on the one or more ICs;

wherein the one or more ICs are further configured to:

generate a first 80 MHz segment of the first portion of the PHY preamble using the first N*256-point IDFT calculator,

generate a second 80 MHz segment of the first portion of the PHY preamble using the second N*256-point IDFT calculator,

generate a first 80 MHz segment of the PHY data portion using the first N*256-point IDFT calculator, and

generate a second 80 MHz segment of the PHY data portion using the second N*256-point IDFT calculator.

19. The apparatus of claim 11 , wherein N is four.

20. The apparatus of claim 19 , wherein:

the first OFDM tone spacing is 312.5 kHz; and

the second OFDM tone spacing is 78.125 kHz.

21. The apparatus of claim 11 , further comprising:

a medium access control (MAC) processing unit implemented on the one or more integrated circuits; and

a physical layer (PHY) processing unit coupled to the MAC processing unit, the PHY processing unit implemented on the one or more integrated circuits;

wherein the PHY processing unit is configured to

generate the first portion of the PHY preamble to include the first plurality of OFDM symbols,

generate the second portion of the PHY preamble to include the second plurality of OFDM symbols, and

generate the PHY data portion of the PHY data unit to include the one or more third OFDM symbols.