ISSN (Print) : 2319-5940 ISSN (Online) : 2278-1021 International Journal of Advanced Research in Computer and Communication Engineering Vol. 2, Issue 11, November 2013 Copyright to IJARCCE www.ijarcce.com 4236 A NEW SLM AND PTS SCHEMES FOR PAPR REDUCTION IN OFDM SYSTEMS Dr.S.P.Vimal 1 , M.Kasiselvanathan 2 and U.Saravanakumar 3 AP (Sr.G), ECE Department, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India 1 AP, ECE Department, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India 2 AP, ECE Department, P.S.G college of Technology, Coimbatore, Tamil Nadu, India 3 Abstract: Orthogonal frequency division multiplexing (OFDM) is a multi carrier modulation technique where the revolution of 4G wireless communication is focused towards OFDM systems. The major drawback of OFDM system is high Peak to average power ratio .The proposed work is based on peak to average power ratio (PAPR) reduction by the implementation of Selective Mapping Technique (SLM) and Partial Transmit Sequence (PTS) methods. Further the work is extended by modifying the SLM and PTS of PAPR by reducing their complexity of the OFDM system. Simulation results show that the complexity is reduced by using newly proposed algorithm than normal schemes. Keywords: OFDM , SLM , PTS ,CCDF I.INTRODUCTION Nowadays the wireless applications are focused towards high data rates. The concept of multi carrier transmission provides high data rates in communication channel. The OFDM is a special kind of multi carrier transmission technique that divides the communication channel into several equally spaced frequency bands. Here the bit streams are divided into many sub streams and send the information over different sub channels. A sub-carrier carrying the user information is transmitted in each band. Each sub carrier is orthogonal with other sub carrier and it is carried out by a modulation scheme. Data‟s are transmitted simultaneously in super imposed and parallel form. The sub carriers are closely spaced and overlapped to achieve high bandwidth efficiency [2]. The main disadvantage of OFDM is high peak to average power ratio. The peak values of some of the transmitted signals are larger than the typical values [1]. High PAPR of the OFDM transmitted signals results in bit error rate performance degradation, inter modulation effects on the sub carriers, energy spilling into adjacent channels and also causes non linear distortion in the power amplifiers. The main work of this paper is to reduce the high peak powers in OFDM systems. Several methods are there to reduce PAPR effectively(15). In this study the concept of selective mapping (SLM)and partial tansmit sequence(PTS) technique is applied to the OFDM symbols to reduce high peak signals[11]. Coding and simulation were carried out for SLM, PTS and their effects on reducing the PAPR were analysed. Also Reduced Complexity approaches for the SLM and PTS techniques were carried out and their performances in reducing the PAPR were performed and analysed[3]. The power signals of all the above work are viewed in complementary cumulative distribution function (CCDF) plot. The results state that the proposed new SLM and PTS method attains a good PAPR reduction and the encoding complexity is reduced by applying the new schemes. II.SELECTIVE MAPPING TECHNIQUE (SLM) Many methods are there to reduce the PAPR , but both complexity and redundancy are high and only small gains in PAPR are achieved[12]. When the phases of different sub-carriers add up in phase the possibility of PAPR being high is for sure. Hence one method to reduce the in-phase addition is to change the phase before converting the frequency domain signal into time domain[13]. Hence before taking the N point IDFT each block of input is multiplied by an φ vector of length N. Now there is a possibility that the PAPR may turn low. Fig 1 : Scheme of a Modulator with Selective Mapping The figure 1 shows the scheme of a modulator with selective mapping technique. The algorithm for selective mapping technique is as follows: Step 1: Get the input vector(X) of length D and let N=integer Step2: for i=1: N Step 2.1: Generate φ (i) of length D Step 2.2: Multiply φ (i) with the input vector and