Using hyperbolic tangent sigmoid transfer function for companding transform in OFDM system

OFDM (Orthogonal frequency division multiplexing) is one of the key techniques for 4th generation high data rate communications system. However OFDM suffers from high peak-to-average power ratio (PAPR) which substantially degrades the efficiency of a linear power amplifier. A new nonlinear companding transform using hyperbolic tangent sigmoid transfer function is proposed for PAPR reduction in this paper. The proposed method expands the small signals and compresses the peak signals in the time domain simultaneously without changing the average power. Computer simulation based on MATLAB shows that the proposed method gains more peak reduction and improves the BER (bit error ratio) performance slightly, compared with the Huang companding method.