A communication device assigns i) a first orthogonal frequency division multiplex (OFDM) tone block for a communication channel to a first communication device, and ii) a second OFDM tone block to a second communication device. The first OFDM tone block and the second OFDM block each span less than or equal to 10 MHz, and are both within a subchannel that spans a 20 MHz. The communication device generates an orthogonal frequency division multiple access (OFDMA) physical layer (PHY) data unit for transmission in the communication channel. The OFDMA PHY data unit is generated to include: a legacy preamble portion having legacy signal field that spans the subchannel; and a data portion that includes i) first data for the first communication device modulated to the first OFDM tone block, and second data for the second communication device modulated to the second OFDM tone block.