Tone reordering in a wireless communication system

1. A method, comprising:

generating, at a communication device, a physical layer (PHY) data unit for transmission via a communication channel, including generating orthogonal frequency division multiplexing (OFDM) symbols to be included in the PHY data unit, wherein generating each of some of the OFDM symbols includes:

encoding, at a communication device, information bits to be included in the OFDM symbol to generate two or more low density parity check (LDPC) code words to be included entirely in the OFDM symbol;

parsing, at the communication device, content of the two or more LDPC code words into a first frequency segment corresponding to a first subband of the communication channel and a second frequency segment corresponding to a second subband of the communication channel;

for the first frequency segment,

mapping, at the communication device, first content of the two or more LDPC code words to first constellation points corresponding to first OFDM tones in the first subband of the communication channel, and

reordering, at the communication device, the first OFDM tones such that the first content of the two or more LDPC code words is distributed over the first OFDM tones within the first subband of the communication channel; and

for the second frequency segment,

mapping, at the communication device, second content of the two or more LDPC code words to second constellation points corresponding to second OFDM tones in the second subband of the communication channel, and

reordering, at the communication device, the second OFDM tones such that the second content of the two or more LDPC code words are distributed over the second OFDM tones within the second subband of the communication channel.

2. The method of claim 1 , wherein:

reordering the first OFDM tones includes reordering bits in the first content prior to mapping the first content to the first constellation points such that, after mapping the first content to the first constellation points, the first content is distributed over the first OFDM tones within the first subband of the communication channel; and

reordering the second OFDM tones includes reordering bits in the second content prior to mapping the second content to the second constellation points such that, after mapping the second content to the second constellation points, the second content is distributed over the second OFDM tones within the second subband of the communication channel.

3. The method of claim 2 , wherein:

reordering bits in the first content comprises reordering first blocks of bits in the first content, each first block corresponding to a constellation point among the first constellation points; and

reordering bits in the second content comprises reordering second blocks of bits in the second content, each second block corresponding to a constellation point among the second constellation points.

4. The method of claim 1 , wherein:

reordering the first OFDM tones includes reordering the first constellation points after mapping the first content to the first constellation points; and

reordering the second OFDM tones includes reordering the second constellation points after mapping the second content to the second constellation points.

5. The method of claim 1 , wherein:

the first OFDM tones are reordered such that adjacent blocks of bits in the first content, prior to mapping the first content to the first constellation points, correspond to first OFDM tones that are separated in frequency by a minimum tone distance; and

the second OFDM tones are reordered such that adjacent blocks of bits in the second content, prior to mapping the second content to the second constellation points, correspond to second OFDM tones that are separated in frequency by the minimum tone distance.

6. The method of claim 5 , wherein the minimum tone distance is at least three tones.

7. The method of claim 6 , wherein the minimum tone distance is at least six tones.

8. The method of claim 1 , wherein:

the PHY data unit is a multi-user data unit including independent data for at least i) a first user and ii) a second user, wherein data for the first user is encoded using binary convolutional coding (BCC), and data for the second user is encoded using low density parity check (LDPC) coding; and

reordering OFDM tones is performed only for OFDM tones corresponding to the second user.

9. The method of claim 1 , further comprising parsing, at the communication device, the information bits into a plurality of spatial streams.

10. The method of claim 9 , further comprising applying space-time block coding to the plurality of spatial streams to generate a plurality of space-time streams.

11. A communication device, comprising:

a wireless network interface device configured to generate a physical layer (PHY) data unit for transmission via a communication channel, including generating orthogonal frequency division multiplexing (OFDM) symbols to be included in the PHY data unit, wherein the wireless network interface device includes:

one or more low density parity check (LDPC) encoders configured to encode information bits to be included in an OFDM symbol to generate two or more LDPC code words to be included entirely in the OFDM symbol;

a frequency segment parser configured to parse content of the two or more LDPC code words into a first frequency segment corresponding to a first subband of the communication channel and a second frequency segment corresponding to a second subband of the communication channel;

a constellation mapper configured to

map first content of the two or more LDPC code words to first constellation points corresponding to first OFDM tones in the first subband of the communication channel, and

map second content of the two or more LDPC code words to second constellation points corresponding to second OFDM tones in the second subband of the communication channel;

a tone ordering unit configured to

reorder the first OFDM tones such that the first content of the two or more LDPC code words is distributed over the first OFDM tones within the first subband of the communication channel, and

reorder the second OFDM tones such that the second content of the two or more LDPC code words are distributed over the second OFDM tones within the second subband of the communication channel.

12. The communication device of claim 11 , wherein:

an output of the tone ordering unit is coupled to an input of the constellation mapper; and

the tone ordering unit is configured to

reorder bits in the first content such that, after the constellation mapper maps the first content to the first constellation points, the first content is distributed over the first OFDM tones within the first subband of the communication channel, and

reorder bits in the second content such that, after the constellation mapper maps the first content to the first constellation points, the second content is distributed over the second OFDM tones within the second subband of the communication channel.

13. The communication device of claim 12 , wherein the tone ordering unit is configured to:

reorder first blocks of bits in the first content, each first block corresponding to a constellation point among the first constellation points; and

reorder second blocks of bits in the second content, each second block corresponding to a constellation point among the second constellation points.

14. The communication device of claim 11 , wherein:

an output of the constellation mapper is coupled to an input of the tone ordering unit; and

the tone ordering unit is configured to

reorder the first constellation points output by the constellation mapper, and

reorder the second constellation points output by the constellation mapper.

15. The communication device of claim 11 , wherein the tone ordering unit is configured to:

reorder the first OFDM tones such that adjacent blocks of bits in the first content, prior to the constellation mapper mapping the first content to the first constellation points, correspond to first OFDM tones that are separated in frequency by a minimum tone distance; and

reorder the second OFDM tones such that adjacent blocks of bits in the second content, prior to the constellation mapper mapping the second content to the second constellation points, correspond to second OFDM tones that are separated in frequency by the minimum tone distance.

16. The communication device of claim 15 , wherein the minimum tone distance is at least three tones.

17. The communication device of claim 16 , wherein the minimum tone distance is at least six tones.

18. The communication device of claim 11 , wherein:

the PHY data unit is a multi-user data unit including independent data for at least i) a first user and ii) a second user;

the wireless network interface device further comprises one or more binary convolutional coding (BCC) encoders; and

the wireless network interface device is configured to

encode data for the first user using the one or more BCC encoders,

encode data for the second user using the one or more LDPC encoders, and

not apply the tone ordering unit to OFDM tones corresponding to the first user.

19. The communication device of claim 11 , wherein the wireless network interface device further comprises a spatial stream parser configured to parse the information bits into a plurality of spatial streams.

20. The communication device of claim 19 , wherein the wireless network interface device further comprises a space-time block coder to generate a plurality of space-time streams from the plurality of spatial streams.