A method for decoding an orthogonal frequency division multiplex (OFDM) data unit is described. OFDM symbols of the OFDM data unit are received that include a first OFDM symbol that corresponds to a legacy signal field followed by a second OFDM symbol that corresponds to a candidate signal field. It is determined whether the candidate signal field corresponds to a repetition of the legacy signal field. At least some of the OFDM symbols of the OFDM data unit are decoded according to a first communication protocol indicated by the determination of whether the candidate signal field corresponds to the repetition of the legacy signal field.