Signaling PHY preamble formats

1. A method, comprising:

determining, at a communication device, a format according to which a physical layer (PHY) data unit is to be generated, wherein the determined format is selected from a set of multiple PHY formats defined by a communication protocol;

selecting, at the communication device: i) a length value to be included in a field in a legacy portion of a PHY preamble of the PHY data unit, and ii) a phase of modulation of an orthogonal frequency division modulation (OFDM) symbol in a non-legacy portion of the PHY preamble, wherein:

the length value and the phase of modulation are selected to correspond to the determined format,

the length value is not divisible by three,

a first value of a remainder resulting from dividing the length value by three corresponds to a first subset of formats among the multiple PHY formats,

the first subset of formats includes a multi-user format,

a second value of the remainder resulting from dividing the length value by three corresponds to a second subset of one or more formats among the multiple PHY formats, and

when the determined format belongs to the first subset, the phase of modulation of the OFDM symbol in the non-legacy portion of the PHY preamble indicates whether the PHY data unit conforms to the multi-user format;

generating, at the communication device, the PHY data unit to include the selected length value in the field in the legacy portion of the PHY preamble and to modulate the OFDM symbol in the non-legacy portion of the PHY preamble with the selected phase; and

transmitting, by the communication device, the PHY data unit.

2. The method of claim 1 , wherein:

the PHY preamble includes a signal field in the non-legacy portion of the PHY preamble;

the second subset of one or more formats includes a format in which the PHY preamble includes repeated bits of the signal field; and

the second value of the remainder resulting from dividing the length value by three indicates that the PHY data unit conforms to the format in which the PHY preamble includes repeated bits of the signal field.

3. The method of claim 2 , wherein:

the OFDM symbol in the non-legacy portion of the PHY preamble is a first OFDM symbol in the signal field;

the signal field includes a second OFDM symbol;

the first OFDM symbol follows the second OFDM symbol in the non-legacy portion of the PHY preamble; and

selecting the phase of modulation comprises selecting the phase of modulation of the first OFDM symbol.

4. An apparatus, comprising:

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

determine a format according to which a physical layer (PHY) data unit is to be generated, wherein the determined format is selected from a set of multiple PHY formats defined by a communication protocol,

select i) a length value to be included in a field in a legacy portion of a PHY preamble of the PHY data unit, and ii) a phase of modulation of an orthogonal frequency division modulation (OFDM) symbol in a non-legacy portion of the PHY preamble, wherein:

the length value and the phase of modulation are selected to correspond to the determined format,

the length value is not divisible by three,

a first value of a remainder resulting from dividing the length value by three corresponds to a first subset of formats among the multiple PHY formats,

the first subset of formats includes a multi-user format,

a second value of the remainder resulting from dividing the length value by three corresponds to a second subset of one or more formats among the multiple PHY formats,

the second subset of formats includes a multi-user format, and

when the determined format belongs to the first subset, the phase of modulation of the OFDM symbol in the non-legacy portion of the PHY preamble indicates whether the PHY data unit conforms to the multi-user format;

wherein the one or more IC devices are further configured to:

generate the PHY data unit to include the selected length value in the field in the legacy portion of the PHY preamble and to modulate the OFDM symbol in the non-legacy portion of the PHY preamble with the selected phase, and

transmit the data unit.

5. The apparatus of claim 4 , wherein:

the one or more IC devices are further configured to generate the PHY preamble to include a signal field in the non-legacy portion of the PHY preamble;

the second subset of one or more formats includes a format in which the PHY preamble includes repeated bits of the signal field; and

the second value of the remainder resulting from dividing the length value by three indicates that the PHY data unit conforms to the format in which the PHY preamble includes repeated bits of the signal field.

6. The apparatus of claim 5 , wherein:

the OFDM symbol in the non-legacy portion of the PHY preamble is a first OFDM symbol in the signal field;

the one or more IC devices are further configured to generate the signal field to include a second OFDM symbol;

the first OFDM symbol follows the second OFDM symbol in the non-legacy portion of the PHY preamble; and

the one or more IC devices are further configured to select the phase of modulation of the first OFDM symbol.

7. The apparatus of claim 4 , wherein the network interface device includes:

a media access control (MAC) processor implemented on the one or more IC devices; and

a physical layer (PHY) processor implemented on the one or more IC devices, the PHY processor being coupled to the MAC processor.

8. The apparatus of claim 7 , wherein:

the PHY processor comprises a plurality of transceivers.

9. The apparatus of claim 8 , further comprising:

a plurality of antennas coupled to the plurality of transceivers.