Performance Comparison of Coded OFDM with DFT-Precoding over Nonlinear Channels

Recent wireless communications systems adopt orthogonal frequency-division multiplexing (OFDM) signaling mainly due to its robustness against fading channels with simple receiver structure. However, it results in poor power amplifier (PA) efficiency or otherwise suffers from severe nonlinear distortion since the transmit signals have high peak-to-average power ratio (PAPR). To mitigate this, DFT-precoded OFDM has been adopted in the uplink of the Long Term Evolution (LTE) standard, which virtually forms single-carrier signals and thus generates lower PAPR than the original OFDM. Nevertheless, the insertion of precoding for OFDM generally complicates the design of optimal detection and suboptimal detection is usually employed. Therefore, the DFT- precoded OFDM with suboptimal detection shows performance inferior to the original OFDM over frequency-selective fading channels when both the systems are protected by channel coding. This observation raises a question if the DFT-precoded OFDM system can outperform OFDM when nonlinearity associate with PA is also considered. In this work, we compare the performance of coded OFDM with and without DFT precoding where both PA nonlinearity and frequency selectiveness of channels are taken into account.