PAPR Analysis of Class-III SLM Scheme Based on Variance of Correlation of Alternative OFDM Signal Sequences

Selected mapping (SLM) is a well-known peak-to-average power ratio (PAPR) reduction technique for orthogonal frequency division multiplexing (OFDM) systems. Recently, a low-complexity SLM scheme, called Class-III SLM scheme, was proposed, which performs only one inverse fast Fourier transform (IFFT) to generate alternative OFDM signal sequences. By randomly selecting the cyclic shift and rotation values, Class-III SLM scheme can generate up to N³ alternative OFDM signal sequences, where N is the IFFT size. However, all N³ alternative OFDM signal sequences do not achieve good PAPR reduction performances. Therefore, an efficient selection method of good rotation and cyclic shift values is needed, which results in good PAPR reduction performance. In this letter, a selection method of cyclic shift values is proposed, which is optimal in terms of minimizing the variance of correlation values between alternative OFDM signal sequences. It is also shown that rotation values are useless when U ≤ N/8, where U is the number of alternative OFDM signal sequences. Also, a selection method of proper rotation values when U > N/8 is proposed. Simulation results show that the proposed method achieves the optimal PAPR reduction performance. In addition, the proposed scheme requires less memory and side information than random scheme.

I. Introduction

ORTHOGONAL frequency division multiplexing (OFDM) is a popular multicarrier modulation technique. Because of the orthogonality of its subcarriers, a receiver can recover the transmitted data without interference. Due to its robustness against multipath fading, OFDM has been adopted as a standard technique for various wireless communication systems such as IEEE 802.11 (WLAN), IEEE 802.16 (WiMAX), and long term evolution (LTE). However, it has a high peak-to-average power ratio (PAPR) problem. When OFDM signals with high PAPR pass through nonlinear high power amplifier, they experience in-band distortion and out-of-band radiation. Thus, in order to reduce PAPR, many schemes have been proposed such as selected mapping (SLM) [1], partial transmit sequence [2], and tone reservation [3].