OFDM시스템에서 PAPR 감소를 위한 낮은 복잡도를 가지는 개선된 PTS 알고리즘

Abstract

The orthogonal frequency division multiplexing (OFDM) technique has drawn much recent attention, especially in the field of wireless communications. For wireless applications, an OFDM-based system can be of interest because it provides greater immunity to multipath fading and impulse noise, and eliminates the need for equalizers, while efficient hardware implementation can be realized using fast Fourier transform (FFT) techniques. A major problem in the RF portion of a multicarrier transmitter is Gaussian-like time domain signals with relatively high peak-to-average power ratio (PAPR). These peaks can lead to saturation in the high power amplifier (HPA) which in turn distorts the signal and reduces the HPA efficiency. To address this problem, numerous techniques have appeared in the literature based on signal and/or data modification. Among the techniques proposed for PAPR mitigation, partial transmit sequence (PTS) technique can improve the PAPR performance of an OFDM signal. As the conventional PTS (C-PTS) technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub-blocks. In order to reduce the computational complexity, iterative flipping PTS (I-PTS) and adaptive PTS (A-PTS) are proposed. This thesis presents a new PTS technique using a phase factor searching algorithm that has a considerable complexity savings for determining the optimum phase factors without increased side information. Moreover, the complexity of the proposed PTS technique can be further reduced if the preset threshold is used. Simulation results show that the proposed PTS technique achieves a significant reduction in search complexity with little PAPR performance degradation.