Physical layer frame format for WLAN

A method for generating a physical layer (PHY) data unit that conforms to a first communication protocol, the method comprising:

• generating, at a first communication device, a PHY preamble of the PHY data unit to include:
• a first orthogonal frequency division multiplexing (OFDM) symbol corresponding to a legacy signal field, the legacy signal field including i) a length subfield, and ii) a rate subfield, wherein the length subfield and the rate subfield indicate a duration of the PHY data unit, and wherein the legacy signal field is formatted according to a legacy second communication protocol,
• a second OFDM symbol corresponding to a duplicate of the legacy signal field, the second OFDM symbol following the first OFDM symbol in time, and
• a plurality of additional OFDM symbols corresponding to a non-legacy signal field;
• in response to determining that the PHY data unit is to be generated according to a non-range extension PHY mode defined by the first communication protocol, generating, at the first communication device, the plurality of additional OFDM symbols to use a first modulation pattern;
• and
• in response to determining that the PHY data unit is to be generated according to a range extension PHY mode define by the first communication protocol, generating, at the first communication device, the plurality of additional OFDM symbols to use a second modulation pattern to signal that the PHY data unit is generated according to the range extension PHY mode;
• generating, at the communication device, a PHY data portion of the PHY data unit;
• and
• transmitting, by the communication device, the PHY data unit via a wireless communication channel.