A method for generating a data unit for transmission via a communication channel, the data unit conforming to a first communication protocol, the method comprising: generating a preamble of the data unit, wherein the preamble includes a first signal field having information that indicates a duration of the data unit, the first signal field being formatted such that the first signal field is decodable by a receiver device that conforms to a second communication protocol but does not conform to the first communication protocol to determine the duration of the data unit based on the first field, the preamble includes a second signal field having a first orthogonal frequency division multiplexing, OFDM, symbol and a second OFDM symbol, the first OFDM symbol is modulated such that a receiver device that conforms to a third communication protocol but does not conform to the first communication protocol will assume that the data unit conforms to the second communication protocol, and the second OFDM symbol is modulated with a 90-degree rotation as compared to the first OFDM symbol such that a receiver device that conforms to the first communication protocol can determine that the data unit conforms to the first communication protocol; and generating a data portion of the data unit that conforms to the first communication protocol and does not conform to either (i) the second communication protocol or (ii) the third communication protocol. generating a preamble of the data unit, wherein the preamble includes a first signal field having information that indicates a duration of the data unit, the first signal field being formatted such that the first signal field is decodable by a receiver device that conforms to a second communication protocol but does not conform to the first communication protocol to determine the duration of the data unit based on the first field, the preamble includes a second signal field having a first orthogonal frequency division multiplexing, OFDM, symbol and a second OFDM symbol, the first OFDM symbol is modulated such that a receiver device that conforms to a third communication protocol but does not conform to the first communication protocol will assume that the data unit conforms to the second communication protocol, and the second OFDM symbol is modulated with a 90-degree rotation as compared to the first OFDM symbol such that a receiver device that conforms to the first communication protocol can determine that the data unit conforms to the first communication protocol; and the preamble includes a first signal field having information that indicates a duration of the data unit, the first signal field being formatted such that the first signal field is decodable by a receiver device that conforms to a second communication protocol but does not conform to the first communication protocol to determine the duration of the data unit based on the first field, the preamble includes a second signal field having a first orthogonal frequency division multiplexing, OFDM, symbol and a second OFDM symbol, the first OFDM symbol is modulated such that a receiver device that conforms to a third communication protocol but does not conform to the first communication protocol will assume that the data unit conforms to the second communication protocol, and the second OFDM symbol is modulated with a 90-degree rotation as compared to the first OFDM symbol such that a receiver device that conforms to the first communication protocol can determine that the data unit conforms to the first communication protocol; and generating a data portion of the data unit that conforms to the first communication protocol and does not conform to either (i) the second communication protocol or (ii) the third communication protocol.