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Motivated by the high capacity of multiple-input multiple-output (MIMO) broadcast channels, this paper investigates the use of only linear signal processing (and hence conventional codec) at the transmitter and receivers to realize the rich diversity (or capacity) of the channel. In particular, we combine a recently developed orthogonal space division multiplexing (OSDM) scheme and orthogonal frequency division multiplexing (OFDM) to decompose per-subcarrier channel into many uncoupled single-user spatial modes. Issue like channel mismatches arising from pilot-aided channel estimation and Doppler spread is examined, and a method exploiting the frequency correlation of the channel to reduce processing complexity is proposed. Simulation results show that for HiperLAN II, the scheme can achieve good performance with four simultaneous downlink users at Doppler spread of 40 Hz (or speed of 8.5 km/h at 5 GHz).