Space-Frequency Shift Keying in Rapidly Time-Varying MIMO OFDM Channels

In this paper, the scheme to achieve transmit diversity in the rapidly time-varying (RTV) multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) channel is studied. Concretely, two schemes named space-frequency shift keying (SFSK) and generalized SFSK (GSFSK) are proposed. In the proposed SFSK, the space-frequency dispersion matrices are constructed by the circular shifting of sparse vectors, and each modulation symbol is transmitted in one space- frequency resource block according to the pattern determined by the activated dispersion matrix. While in the proposed GSFSK, multiple dispersion matrices are activated to modulate multiple symbols in one space- frequency resource block simultaneously, and thereby a higher spectral efficiency is achieved. Next, the capacity of the proposed schemes to achieve the transmit diversity gain is validated through the analysis of the asymptotic diversity order. Moreover, a correlation-based detector is presented to reduce the detection complexity of both SFSK and GSFSK. Finally, the performance of the proposed schemes are demonstrated by computer simulations.