In a method for detecting a clock rate of a data unit, the data unit is received via a communication channel. The data unit includes i) a first preamble portion and ii) an orthogonal frequency division multiplexing (OFDM) portion following the first preamble portion. The OFDM portion includes a second preamble portion including one or more long training fields. Based on the first preamble portion, whether a clock rate of the OFDM portion is a first clock rate or a second clock rate lower than the first clock rate is determined based on the first preamble portion.