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Block-wise Alamouti schemes for OQAM-OFDM systems with complex orthogonality

Offset quadrature amplitude modulation-based orthogonal frequency division multiplexing (OFDM) systems cannot be directly combined with the Alamouti code because of the intrinsic imaginary interference. In this paper, we propose a block-wise space-frequency block coding (SFBC) scheme and a block-wise space-time block coding (STBC) scheme for offset quadrature amplitude modulation-based OFDM systems, which achieve bit error rate performances that are close to OFDM systems. The proposed schemes satisfy the orthogonality condition of the Alamouti code in the complex field with guard band/intervals. To improve the spectral efficiency of the block-wise SFBC scheme, we also consider the case without the guard band. It is observed that only the two innermost subcarriers do not satisfy the complex orthogonality condition when the guard band is removed. Then, a simple equalization scheme is proposed to independently equalize the two innermost subcarriers. Simulation results show that the block-wise SFBC scheme works well under channels with mild-to-moderate frequency selectivity, and the block-wise (STBC ) scheme suffers less than 1 dB loss under severe frequency selective channels at the bit error rate of 10 − 3, when only a simple one tap zero-forcing equalizer is employed. Copyright © 2016 John Wiley & Sons, Ltd.