Rotated MC-Cyclic Antenna Frequency Spread: Effect of Rotations in Correlated MIMO-OFDM Systems

MIMO systems, although they offer high transmission rates and robustness against channel fading, often suffer from antenna correlations. In this paper, we investigate the effect of spreading and symbol rotation on a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system with correlations. A novel family of orthogonal spreading matrices multi-carrier-cyclic antenna frequency spread (MC-CAFS) - is used for spreading. These matrices make use of both the spatial and the frequency dimensions offered by MIMO-OFDM. We describe how transmit vector rotations can be applied to MC-CAFS spreading matrices. Three new rotation methods are introduced in this paper. We compare the performance of MC-CAFS (with and without rotations) with that of the unspread system and with multi-carrier-code division multiplexing (MIMO-MC-CDM), also with and without rotations