A low-complexity cross-antenna rotation and inversion scheme for PAPR reduction of STBC MIMO-OFDM systems

In this paper, a reduced-complexity cross-antenna rotation and inversion (CARI) scheme based on the cross-entropy (CE) method is proposed for the reduction of peak-to-average power ratio (PAPR) in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with space-time block coding (STBC). A few PAPR reduction techniques for STBC MIMO-OFDM systems have been proposed in the literature, among which the CARI technique can significantly reduce the PAPR by fully utilizing additional degrees of freedom provided by employing multiple transmit antennas. However, the CARI technique requires an exhaustive search over all combinations of rotation and inversion, whose complexity increases exponentially with the number of subblocks. To simultaneously reduce the complexity and offer lower PAPR, the PAPR reduction with CARI technique is formulated as a combinatorial optimization problem and then the CE method is applied to search the optimal combination of rotation and inversion. Simulation results show that the proposed CE-based scheme is an efficient method to greatly reduce the complexity for larger numbers of subblocks while still achieving significant PAPR reduction of STBC MIMO-OFDM systems.