An orthogonal-frequency division multiplexed (OFDM) transmitter is configured to transmit a data unit in accordance with a multiple-input multiple-output (MIMO) technique over a wideband channel comprising a 20 MHz channel and another channel using a plurality of spatially diverse antennas. The transmitter is further configured to include in the data unit, a parameter indicating a modulation and coding scheme and a parameter indicating number of spatial streams. Each of the spatial streams is encoded and beamformed for receipt by one or more different receiving stations.