PAR Reduction in SU/MU-MIMO OFDM Systems Using OPF Precoding Over the Nonlinearity of SSPA

Abstract

Orthogonal frequency division multiplexing (OFDM) system suffers from a high peak-to-average (power) ratio (PAR) which leads to power inefficiency in radio frequency section and large performance degradation of system due to the nonlinearity of high power amplifiers (HPA). In this paper, a new downlink transmission scheme is designed based on orthogonal periodic function (OPF) precoding to achieve low PAR and investigated for single user and multi-user multiple-input multiple-output wireless systems. It is shown (through mathematical analysis and computer simulations) that the proposed transmission scheme can provide a significant PAR reduction using decorrelation, phase-rotation and orthogonality properties of OPF precoding, while it does not change power spectral levels or error performances due to the unitary property when compared with the normal OFDM systems with linear HPA. The OPF precoding outperforms existing precoding schemes when nonlinear solid state power amplifier (SSPA) is considered with several practical values of input back-off (IBO). Computer simulations show that the OPF precoding can achieve 3.1 and 4 dB PAR gain, while 2.2 and 1 dB SNR gain for IEEE 802.11a and DVB-T systems respectively. Moreover, OPF precoding leads to a total degradation improvement from 0.13 to 1.53 dB for 16 QAM, considering an SSPA with IBO = 8---4 dB respectively. OPF precoding does not increase computational complexity when compared with the existing precoding methods. It is shown that the performance of the proposed precoding is independent of modulation schemes and can work for any number of subcarriers.