A plurality of different OFDM tone blocks for a wireless local area network (WLAN) communication channel are assigned to a plurality of devices. An OFDMA data unit is generated, the OFDMA unit including a preamble portion and a data portion, the preamble portion having at least i) a first legacy portion that corresponds to at least a first OFDM tone block, ii) a second legacy portion that corresponds to a second OFDM tone block, iii) a first non-legacy portion that corresponds to the first OFDM tone block, iv) a second non-legacy portion that corresponds to the second OFDM tone block, and v) a third non-legacy portion that corresponds to a third OFDM tone block. The first OFDM tone block and the second OFDM tone block are separated in frequency by at least the third OFDM tone block.