In a wireless communication system in which communication devices exchange information utilizing data units that conform to a first format, wherein the first format includes a short training field (STF) spread with a first spread code, a method for generating a physical layer (PHY) data unit that conforms to a second format includes generating a first portion of the PHY data unit to indicate the PHY data unit conforms to the second format. The first portion of the PHY data unit includes an STF spread with a second spread code different than the first spread code. The method also includes generating a second portion of the PHY data unit according to the second format. The second portion of the PHY data unit includes PHY information elements not specified by the first format.