Multiuser Precoded OFDM System over Nonlinear Power Amplifier

The presence of a nonlinear power amplifier (NPA) in an orthogonal frequency-division multiplexing (OFDM) system can introduce distortion and spectral regrowth, leading to the degradation of the system's signal quality and an increase in interference. In this paper, we investigate the impact of NPA in multi-user multiple-input multiple-output OFDM (MU-MIMO-OFDM) systems operating over finite impulse response (FIR) and infinite impulse response (IIR) fading channels. MU-MIMO-OFDM systems are sought after for their high data rates and spectral efficiency. However, in the downlink MU-MIMO-OFDM system, performance degradation occurs when nonlinear conditions manifest in the transmitter's NPA, especially with an increasing number of users. This degradation is reflected in the bit error rate (BER) performance. To mitigate this issue, we explore the application of multiuser precoding in the MU-MIMO-OFDM system to reduce interference in signal detection. We analyze BER performance while considering various system parameters, including the number of users, transmitting and receiving antennas, and NPA parameters. Our findings reveal that NPA, especially when combined with IIR, significantly degrades system performance and saturates the BER in high signal-to-noise ratio (SNR) regions.