Space-time/frequency coding (SFC) can achieve the spatial and multipath diversities for an MIMO-OFDM system by coding across subcarriers, multiple antennas, and/or multiple OFDM symbols, where an interesting method to achieve the multipath diversity is repeating across subcarriers proposed by Su et al. Lately, a family of space-time-frequency codes with single-symbol ML decoding have been proposed by Zhang et al to achieve both full spatial and multipath diversities by using orthogonal space-time block codes (OSTBC) across multiple antennas and OFDM symbols and in the meantime repeating across the subcarriers. The main goal of this paper is to modify the repeating process and adjust their phases by a Chu sequence so that the peak-to-average power ratio (PAPR) of the OFDM system is reduced for any SFC from the repeating and in the meantime, the full spatial and multipath diversities are maintained. In this paper, we also generalize the space-time- frequency coding by Zhang et al from using OSTBC to using linearly transformed quasi-orthogonal space-time block codes (QOSTBC) that possesses higher rate than the OSTBC for more than two transmit antennas, fast ML decoding and full spatial and multipath diversities.
['Zhefeng Li', 'Xiang-Gen Xia']
PAPR Reduction for Space-Time-Frequency Coded MIMO-OFDM Systems