HPA Nonlinearity Reduction by Joint Predistorter and Tone-Reservation with Null Subcarriers in WiMAX Systems

Due to the nonlinear effect caused by the high power amplifier (HPA), wireless communication system suffers from the in-band distortion and out-band spectrum regrowth. For orthogonal frequency division multiplexing (OFDM) systems, the high peak to average power ratio (PAPR) would lead to HPA nonlinearity or inefficiency. Compared to traditional PAPR reduction methods, the tone reservation with null subcarriers method (TRNS) is a distortionless PAPR reduction method, which utilizes a part of null subcarriers to reduce PAPR without any side information. In this paper, we propose a joint scheme by predistorter and TRNS method for OFDM system. The main idea of proposed scheme is to relax constraints of the predistorter design after reducing the PAPR of OFDM signals, so that the HPA can achieve a higher saturation point and a bigger dynamic range to increase the HPA efficiency. Simulation results show that the proposed method can improve the BER performance, especially under lower input back-off (IBO) constraint, at IBO=3dB and SNR level of 10^-3, the joint scheme can achieve 5 dB performance gain.