A preamble of physical layer (PHY) data unit includes a first legacy portion and a first non-legacy portion that follows the first legacy portion. The first non-legacy portion includes i) a first orthogonal frequency division multiplexing (OFDM) symbol that immediately follows the first legacy portion and that is modulated using binary phase shift keying (BPSK), and ii) a second OFDM symbol that immediately follows the first OFDM symbol and that is modulated using BPSK modulation rotated by 90 degrees (Q-BPSK). The modulation of the first and second OFDM symbols indicates to a receiver device that conforms to a first communication protocol that the data unit conforms to the first communication protocol. The first OFDM symbol being modulated using BPSK modulation causes a receiver device that conforms to a second communication protocol to determine that the PHY data unit conforms to a third communication protocol.