I. Introduction
MUlti-carrier techniques such as orthogonal frequency-division multiplexing (OFDM) systems are widely used in wireless communications [1], [2]. Compared with single-carrier techniques, multi-carrier techniques have higher spectrum efficiency, and are more resistant to deep fading effect. However, the peak-to-average power ratio (PAPR) is an inherent problem in the multi-carrier system [3]. The design of high power amplifier (HPA) in the transmitter can reduce the PAPR at the expense of lower power efficiency [3], [4].