Abstract
One inherent drawback associated with multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR) at the transmitter’s output, and this usually causes undesirable nonlinear distortions. There have been a number of PAPR reduction techniques proposed for MIMO-OFDM systems, but their computational complexity is too high to be useful for practical applications. Besides, most of them cannot be used for MIMO-OFDM systems with space frequency block coding (SFBC). In this thesis, we propose a low-complexity PAPR reduction scheme for SFBC-based MIMO-OFDM systems. We first multiply the input sequence by a set of phase rotation vectors respectively and then utilize the linear property of SFBC to decompose each resulting sequence into several sub-sequences. After computing the inverse fast Fourier transform (IFFT) to convert each frequency-domain sub-sequence into a time-domain signal, we utilize the IFFT properties to do equivalent SFBC encoding operations in the time-domain for generating candidate signal sets, where the one with the lowest maximum PAPR is selected for transmission. Based on the proposed approach, we can obtain a large number of candidate signal sets by computing only a few IFFTs. Moreover, we reduce the complexity of selecting the optimal candidate signal set by setting a threshold to avoid generating unnecessary candidate signal sets. Simulation results show that, with lower computational complexity, the proposed scheme has comparable PAPR reduction performance to existing schemes for SFBC-based MIMO-OFDM systems.