Abstract: Orthogonal frequency division multiplexing (OFDM) has been adopted as standard beginning with the 4^th generation mobile communication system because of its high-bit-rate transmission capability under frequency selective fading channel conditions. However, a major disadvantage of OFDM is the non-constant envelope signal with a high peak-to-average power ratio (PAPR). The high peak signal in OFDM is distorted through a nonlinear amplifier, which causes bit error ratio (BER) reduction. Many techniques have been developed for reducing PAPR at the cost of inefficient bandwidth usage or throughput because of the additional information about PAPR reduction. We propose a novel method, in which the high peak signal above the threshold of the nonlinear amplification region is nonlinearly downscaled to lower the PAPR. The time slot location and scaling ratio for where and how the high peak baseband OFDM signal is downscaled are transmitted using frequency modulation (FM) combined with OFDM, which requires less additional bandwidth than the previously proposed methods. Simulation results show that the proposed novel method provides a lower PAPR and elicits a better BER performance compared with other conventional methods, because it reduces the PAPR by nonlinear scaling and restores the pre-distorted signal using FM.

Key words: Orthogonal frequency division multiplexing, Peak-to-average power ratio, Nonlinear scaling, Frequency modulation

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