32n d NATIONAL RADIO SCIENCE CONFERENCE (NRSC 2015), March24-26, 2015, October University for Modern Sciences and Arts, Egypt cs. SLM Technique Based on Particle Swarm Optimization Algorithm for PAPR Reduction in Wavelet -OFDM Systems Sameh A. Fath/, Mohamed . El-Mahallaw/, Esam A. A. Hagras3 l The Higher Institute of Engineering, EI-Shorouk Academy, Cairo, Egypt, sameh.fathy.eg@ieee.org 2 College of Engineering and Technology, AASTMT, Cairo, Egypt, mahallawy@aast.edu 3 Technical Research Center, Cairo, Egypt, esamhagras _ 2006@yahoo.com ABSTRACT Orthogonal requency division multiplexing (OFDM) system has high spectral eiciency and immunity to requency selective fading channel. So, it has been widely used in modem wireless communication systems. However, the major drawback of OFDM system is the high peak-to-average power ratio (PAPR) of the transmitted signal for large number of subcarriers. Selected mapping (SLM) is one of the most well-known technique to reduce the PAPR in OFDM system, since it can achieve a good PAPR reduction without signal distortion. Moreover, SLM technique can be used with wavelet-OFDM (WOFDM) system to enhance the PAPR performance, while maintaining most of the advantages of the conventional OFDM system. In this paper, an effective PAPR reduction technique using SLM-WOFDM based on particle swarm optimization (PSO) algorithm is proposed. PSO is applied to SLM-OFDM and SLM-WOFDM systems for searching the optimum phase rotation factors. The systems evaluation shows that the proposed PSO based SLM-WOFDM system provides better PAPR reduction compared to PSO based SLM-OFDM, SLM-WOFDM, and conventional SLM-OFDM systems. Keywords: PSG , PAPR , SLM, inverse discrete wavelet transform lDW. I. INTRODUCTION OFDM is a parallel transmission system, where a high rate serial data stream is broken up into a set of low rate substreams, each of which is transmitted over a separate subcarrier. As a result of that, the bandwidth of the subcarriers come to be small compared with the coherence bandwidth of the channel. Consequently, OFDM changes the requency selective fading channel into several lat fading subchannels, which allows for simple equalization [1]. Therefore, OFDM has been widely used in many wireless communication standards [2], [3]. However, a well-known problem of OFDM is its sensitivity to intersymbol interference (lSI) and intercarrier interference (ICI) introduced by the channel variations, where lSI is the effect that the adjacent OFDM symbols exert on each other due to channel delay spread and ICI is the effect that subcariers exert on each other due to channel requency offset. But these problems can be reduced signiicantly by inserting the cyclic prefix (CP) between OFDM symbols. However, the CP has the disadvantage of reducing the spectral eficiency [4]. Generally, OFDM system suffers rom a major problem of large PAPR. In OFDM system, output signal is a linear combination of the data modulated subcarriers that can have very large PAPR. The high PAPR distorts the signal when the OFDM signal is passed through a power ampliier. Reducing the PAPR using a very large linear ampliier range is a conventional solution, which increases system complexity and cost [5]. Recently, various PAPR reduction techniques have been proposed such as selected mapping (SLM) [6], [7], partial transmit sequence (PTS) [8]. The conventional SLM technique is an attractive and eficient technique used to achieve a good PAPR reduction without signal distortion [7]. In WOFDM system, the wavelet transform (WT) is used instead of IFFTIFFT maintaining most of the advantages of the conventional OFDM system with better spectral eiciency and PAPR reduction performance. Also, as in [9], [10] the symbol error rate (SER) of WOFDM system is less compared to conventional OFDM system under certain channel conditions. In this paper, an eicient PAPR reduction technique using a SLM WOFDM is used to reduce the PAPR, then PSO is applied to SLM-WOFDM system for searching the optimum phase rotation factors to achieve better reduction in PAPR and hence leading to more improvement in PAPR reduction performance. PSO is used as one of the evolutionary algorithms (EAs) which are found to be better than the other EA such as genetic algorithm in terms of execution time, simplicity and convergence [11]. Also, PSO based SLM-WOFDM system is compared to PSO based SLM-OFDM system to show the improvement achieved by using WOFDM system instead of OFDM system in PAPR. ISBN 978-1-4799-7723-9/15/$3\.00  2015 IEEE 163