MIMO–OFDM With Nonlinear Power Amplifiers

The influence of nonlinear power amplifiers (PAs) on the performance of multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems is investigated. A “full” MIMO scheme with transmitters (TX) precoding and receivers (RX) decoding is considered. It is shown, under assumption of high order OFDM and frequency selective channel, that the ratio between the useful signal and the nonlinear distortions is proportional to the number of TX antennas, i.e., the influence of the nonlinear distortions decreases as the number of TX antennas increases. The distortion reduction factor (DRF) is proposed as a performance metric for MIMO-OFDM systems with nonlinear PAs. A general formula for signal to distortion and noise ratio is obtained for the nonlinear PA with memory, described by the Wiener-Hammerstein (WH) model. Special cases of MIMO, such as maximum ratio transmission (MRT) and maximum ratio combining (MRC), are considered. A full agreement between the theoretical and simulation results is obtained. The main contribution of this paper is in a statement that TX processing reduces the effect of nonlinear distortions. This is obtained by novel approach for analysis of the MIMO-OFDM systems with nonlinear PAs with memory.