Wireless communications always strive for higher throughput and higher performance. The Multiple Inputs Multiple Outputs (MIMO)- Orthogonal Frequency Division Multiplexing (OFDM) scheme is the key PHYsical (PHY) layer feature of the next generation Wireless Local Area Networks (WLAN) IEEE 802.11ac standards. In this paper, the authors propose a novel MIMO-OFDM scheme based on modulation diversity for IEEE 802.11ac. This proposed scheme jointly optimizes the MIMO-OFDM and modulation diversity together, which makes full use of time diversity, frequency diversity and space diversity. It exhibits high spectral efficiency and low error rate in fading channels.