Efficient Papr Reduction of Ofdm Signal Using Pts Technique with Hybrid Partitioning Method

The high peak-to-average power ratio (PAPR) is one of the major problems of orthogonal frequency division multiplexing (OFDM) systems in wireless transmission. Therefore, partial transmit sequence (PTS), a promising scheme that can provide good PAPR reduction performance, has been proposed for OFDM transmission to eliminate distortion. The PTS method divides the input data block into disjoint sub-blocks, computes Inverse Fourier Transform of the subblocks, rotates the sub-blocks with appropriate phase factors and combines them to form the transmitted signal. This paper presents an enhanced PTS approach that combines two PTS partitioning schemes (adjacent and interleaved) to effectively reduce the PAPR of the OFDM systems. The influence of the proposed approach on performance is investigated by varying the size of the disjoint sub-blocks. The PAPR reduction performance of the proposed PTS method is compared with two well known sub-blocks partitioning schemes, namely, Adjacent Partitioning (AP), Interleaved Partitioning (IP). The various computer simulation results for the various sub-blocks confirmed that the proposed method provides better PAPR reduction performance compared with AP and IP partitioning based PTS scheme. In addition, these PTS schemes largely depend on the chosen size of the partitions. Keyword: adjacent partitioning PTS (AP-PTS), interleaved partitioning PTS (IP-PTS), orthogonal frequency division multiplexing (OFDM), peak-to-average power ratio (PAPR), partial transmit sequences (PTS). INTRODUCTION Orthogonal frequency division multiplexing (OFDM) is a promising multi-carrier modulation technique for achieving high data transmission rate over frequency selective fading channels in wireless communication system [1]. This technique has been widely employed in digital transmission, such as in digital video/audio broadcasting systems and wireless local area networks. Furthermore, OFDM is considered as an attractive transmission technique for fourth-generation wireless mobile communications [2]. However, one of the main drawbacks of the implementation of RF of an OFDM is the high peak to-average power ratio (PAPR) of the transmitted signal. Larger peaks lead to reduced power efficiency, signal distortion, and an increased complexity of a digital-to-analog and analog-to-digital converters [3]. Various methods have been proposed to control the PAPR of the transmitted signals in OFDM systems [4], including deliberate clipping [5], transmit filtering [6], companding [7], block coding [8], partial transmit sequence (PTS) [9], selective mapping (SLM) [10], tone reservation [11], and constellation extension [12]. Probabilistic methods, such as SLM and PTS, can achieve PAPR reduction with only a small rate of data loss [1]. SLM and PTS require numerous IFFTs and rotating phase vector that must be transmitted to achieve high PAPR performance. However, the performance of the system would affect the PAPR reduction in methods such as deliberate clipping; transmit filtering and companding schemes because of signal distortion. Among these methods, PTS is an attractive and well-known scheme that provides less distortion based on combining signal sub-blocks that are multiplied by weighting factors. In addition, the PAPR performance can be improved by multiplying the optimal phase rotating factor [13]. This study focuses on the use of a probabilistic method to reduce the PAPR in an OFDM-based system and proposes an effective PTS method. A modified PTS scheme is compared with other existing ones with varying lengths of disjoint sub-blocks. Furthermore, the proposed PTS method combines two types of sub-block partitioning schemes (adjacent and interleaved) for PAPR reduction in OFDM systems compared with the ordinary PTS scheme. The proposed PTS method can significantly reduce the PAPR with less computational complexity. The paper is organized as follows: Section II presents the PAPR of the OFDM system and the conventional PTS method. Section III presents the sub-block partitioning methods. Section IV explains the proposed PTS method for improved PTS technique. Section V shows the simulation result and Section VI draws a conclusion. PAPR AND THE PTS TECHNIQUE A. PAPR of OFDM signals For be the number of subcarriers, is the frequency index, and is denote a vector of phase shift keying (PSK) or quadrature amplitude modulation (QAM) complex symbols. This vector is transmitted using one OFDM symbol , where the discrete-time index is n. The of the discrete time samples can obtained by taking an point inverse discrete Fourier transform (IDFT). VOL. 9, NO. 12, DECEMBER 2014 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2014 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 2763 To assess the difference in the time domain samples , the PAPR of an OFDM symbol is defined as the ratio of the maximum instantaneous power to the average power [14] where denote the expected value. The complementary cumulative distribution function (CCDF) of the PAPR was employed to evaluate the PAPR reduction [15]