In a method implemented in a communication device configured to transmit PHY data units via a communication channel, first data and second data is received. The first data is modulated according to a first constellation having a first number of constellation points, and the second data is modulated according to a second constellation having a second number of constellation points higher than the first number of constellation points. The first data and the second data is parsed to a plurality of spatial streams such that a first subset of the spatial streams includes at least some of the modulated first data but none of the modulated second data, and a second subset of the spatial streams includes at least some of the modulated second data but none of the modulated first data. A single PHY data unit that includes the plurality of spatial streams is generated.