International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 03 |March -2017
p-ISSN: 2395-0072
www.irjet.net
PAPR Reduction Technique : Partial Transmit Sequence (PTS) Kinjal P. Anand
Electronics and Communication Dr.S. & S .S. Gandhy Government Engineering College, Surat, India ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract -Orthogonal Frequency Division Multiplexing
(OFDM) is a very attractive technique for high-data-rate transmission in wireless and wired applications. One major drawback of OFDM is that the time domain OFDM signal which is a sum of several sinusoids leads to high peak to average power ratio (PAPR).OFDM faces the Peak-toAverage Power Ratio (PAPR) problem which leads to power inefficiency in RF section of the transmitter. Number of techniques has been proposed for reducing the PAPR in OFDM systems. In this paper PTS(Partial transmit sequence) technique proposed for reducing the PAPR.The partial transmit sequences (PTS) scheme achieves an excellent peak-to-average power ratio (PAPR) reduction performance of orthogonal frequency division multiplexing (OFDM) signals at the cost of exhaustively searching all possible rotation phase combinations, resulting in high computational complexity. Key Words: Orthogonal frequency division multiplexing (OFDM), peak-to-average power ratio (PAPR), CCDF, partial transmit sequences, IIFT
1. INTRODUCTION Orthogonal frequency division multiplexing (OFDM) is one of the most attractive technology for fourth generation (4G) wireless communication. The basic principle of OFDM is to split a high-rate data stream into a number of lower rate streams that are transmitted simultaneously over a number of subcarriers. OFDM faces several challenges. The key challenges are large peak to average ratio due to non linearity’s of amplifier; phase noise problems of oscillator, need frequency offset correction in the receiver. Large peak-to-average power (PAP) ratio which distorts the signal if the transmitter contains nonlinear components such as power amplifiers (PAs).This is because power amplifier at transmitter enters into saturation region instead of being in linear region which causes distortion to the transmitted signal which further results in increased BER at the receiver. In other words, the nonlinear distortion causes both in-band and out-of-band interference to signals. Therefore the PAs requires a back off which is approximately equal to the PAPR for distortion-less transmission. This decreases the efficiency for amplifiers. Therefore, reducing the PAPR is of practical interest. Many PAPR reduction methods have been proposed. The associated drawback is the increased power and implementation complexity. OFDM is adopted
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in various communication applications such as, digital video broadcasting (DVB), digital audio broadcasting (DAB) and wireless local area networks (WLAN). As a result, high PAPR of transmitted signals causes nonlinear distortion at high power amplifier (HPA) and reduces its power efficiency. Also, a distortion of the signal leads to degradation of adjacent channel interference and high bit error rate (BER). To avoid the appearance of large PAPR of OFDM signals, different methods for PAPR reduction have been proposed. In this paper, we discuss the PTS technique for PAPR reduction. Among all existing methods, the partial transmit sequence (PTS) is an attractive solution due to its good performance of PAPR reduction In the PTS method, input data symbols are divided into disjointed sub-blocks and the sub-blocks are separately phase-rotated by individually selected phase factors through the process of improving performance of the PAPR. The remainder of this paper is organized as follows. In section 3, some basics about PAPR problem in OFDM is given. Section 4 describes CCDF of OFDM. Section 5 describes Partial Transmit Sequence (PTS) Technique. In Section 6 describe simulation Results. Conclusions is given in section 7.
2.OFDM SYSTEM The transmit signal can be generated by a simple IDFT operation, and at the receiver; a DFT can be performed to recover the transmitted signal. In OFDM systems, a fixed number of successive input data samples are modulated first and then jointly correlated together using IFFT at the transmitter side. IFFT is used to produce orthogonal data subcarriers. Mathematically, IFFT combines all the input signals to produce each signal of the output OFDM symbol. The OFDM signal is obtained by considering data block of N symbols each, where n = [1, 2,…….., N-1] and each symbol is modulated by a subcarrier which is taken from a set of subcarriers, and these subcarriers are chosen such that they are orthogonal to each other. The discrete time domain signal of OFDM is generated by applying N-point IFFT on frequency domain OFDM signal , which can be written as: =
√
Where
∑
, 0 ≤ n ≤ N – 1, is modulated symbol
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