A method for generating a physical layer data unit for transmission via a communication channel, the method comprising: determining pilot tone contribution sequence values for a first set of orthogonal frequency division multiplexing [OFDM] symbols, the first set of OFDM symbols to be included in a signal field of the data unit; determining, pilot tone contribution sequence values for a second set of OFDM symbols, the second set of OFDM symbols to be included in a data portion of the data unit; generating the first set of OFDM symbols to include pilot tones modulated based on the pilot tone contribution sequence values determined for the first set of OFDM symbols; generating the second set of OFDM symbols to include pilot tones modulated based on the pilot tone contribution sequence values determined for the second set of OFDM symbols; generating the signal field to include the first set of OFDM symbols; generating the data portion include the second set of OFDM symbols; and generating the data unit to include at least the (i) signal field, (ii) the data portion, and (iii) a set of one or more training fields between the signal field and the data portion; characterized in that said step of determining pilot tone contribution sequence values for a first set of OFDM symbols includes using a pilot mapping function multiplied by a pseudorandom pilot tone polarity sequence, wherein the pilot mapping function depends on an OFDM symbol index; and said step of determining pilot tone contribution sequence values for a second set of OFDM symbols includes using the pilot mapping function multiplied by the pseudorandom pilot tone polarity sequence. determining pilot tone contribution sequence values for a first set of orthogonal frequency division multiplexing [OFDM] symbols, the first set of OFDM symbols to be included in a signal field of the data unit; determining, pilot tone contribution sequence values for a second set of OFDM symbols, the second set of OFDM symbols to be included in a data portion of the data unit; generating the first set of OFDM symbols to include pilot tones modulated based on the pilot tone contribution sequence values determined for the first set of OFDM symbols; generating the second set of OFDM symbols to include pilot tones modulated based on the pilot tone contribution sequence values determined for the second set of OFDM symbols; generating the signal field to include the first set of OFDM symbols; generating the data portion include the second set of OFDM symbols; and generating the data unit to include at least the (i) signal field, (ii) the data portion, and (iii) a set of one or more training fields between the signal field and the data portion; characterized in that said step of determining pilot tone contribution sequence values for a first set of OFDM symbols includes using a pilot mapping function multiplied by a pseudorandom pilot tone polarity sequence, wherein the pilot mapping function depends on an OFDM symbol index; and said step of determining pilot tone contribution sequence values for a second set of OFDM symbols includes using the pilot mapping function multiplied by the pseudorandom pilot tone polarity sequence.