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PAPR Reduction Method for Block Diagonalization in Multiuser MIMO-OFDM Systems

This paper proposes a peak-to-average power ratio (PAPR) reduction method that maintains an effect of linear precoding by block diagonalization (BD) for multiuser (MU) MIMO-OFDM systems. In the downlink MU-MIMO-OFDM, BD orthogonalizes multiple signals of all users by the linear precoding using channel state information, but the transmitted signal still has high PAPR due to OFDM characteristics. Therefore, BD suffers from waveform distortion caused by a nonlinear transmit power amplifier, especially when the number of transmit antennas is set large enough for the orthogonalization. This paper proposes BD transmission selected mapping (BD-SLM) that can reduce PAPR while maintaining the BD effect. BD-SLM performs the phase shift to modulation signals of all users before the linear precoding. From several phase sequences, it selects a phase sequence that minimizes the peak of the time-domain signals at all transmit antennas. Computer simulations demonstrate that BD-SLM can drastically reduce PAPR in 16-by-4 MIMO-OFDM with four users, and that it can alleviate the performance degradation even when the power amplifier causes nonlinear distortion.