An improved space-time-frequency (STF) code using digital phase sweeping (DPS) is proposed for multi-input multi-output-orthogonal frequency division multiplexing (MIMO-OFDM) systems. It achieves full diversity attainable over frequency-selective channels and works for arbitrary power delay profile. The maximum transmission rate of the proposed code is one symbol per channel use independently of the number of transmit-antennas. We also show that the proposed code has reduced decoding complexity (1/8 of the space-frequency (SF) codes in ,  when the number of transmit-antennas is even). Finally, simulation results are given to show that the proposed code performs better than some known codes in , .