A Pre-Coding Technique to Mitigate PAPR in MIMO-OFDM Systems

Typically, broadband wireless communication systems employ Multiple-Input Multiple-Output (MIMO) with Orthogonal Frequency-Division Multiplexing (OFDM) systems to yield MIMO-OFDM systems. OFDM serves to convert frequency-selective MIMO channels into equivalent or parallel flat MIMO channels, thus decreasing the complexity at the receiver, while simultaneously helping to attain robust high data rate transmission. One of the key challenges faced by researchers in designing a MIMO-OFDM system is how to mitigate Peak-to-Average-Power Ratio (PAPR). The MIMO-OFDM signal can be displayed as the summation of independent complex variables with adjustable phases. When all the variables become in phase a peak of the summation of amplitudes is formed. This leads to amplification difficulties at the transmitter and to high out-of-band radiation in case of non-linear power amplifiers. The nonlinearity arises mainly because of the large input power range into the nonlinear region of the power amplifier. The literature abounds with methods for mitigating PAPR. This paper suggests a useful model for the relation between the input data and output PAPR, and proposes a pre-coding technique model to redistribute the input data. The results shows that the PAPR reduction capability of the pre-coding technique facilitates the MIMO-OFDM system to perform better with a reduced PAPR. Simulation results with BPSK and QPSK modulations exhibit a reduction in PAPR of around 4 $\mathbf{dB}$.