Analysis and reduction of PAPR effect using linear coding in OFDM system

Abstract

A high peak-to-average power ratio (PAPR) is one of the major shortcomings in Orthogonal Frequency Division Multiplexing (OFDM) systems, as it causes nonlinearity distortion in the transmitter, degrading the performance of the system significantly. To overcome PAPR effects for OFDM signals, there are a number of proposed PAPR reduction techniques such as amplitude clipping, clipping and peak windowing, coding, Selective Mapping Technique (SLM), Partial Transmit Sequence (PTS) etc. However, all the proposed methods have some drawbacks, such as out-of-band radiation for clipping method, side information transmission for SLM and PTS methods and low coding rates for coding implementing methods. In this thesis, reduction of the PAPR of OFDM is studied. A new PAPR reduction method is proposed using linear coding technique. The new method does not distort the signal that increases out-of-band radiation, instead uses block coding of the input data and then modifies the coded data iteratively until the PAPR reduces below a certain level. In the proposed method, at first, an input data block is partitioned into sub-blocks. The bits of each sub-block are encoded using Hamming Code. The encoded data are fed to the modulator input. Outputs of Modulator are fed into IFFT blocks which form regular OFDM symbols. The PAPR values of OFDM symbols are calculated and compared with a certain threshold. If the PAPR value is below the threshold, no operation is performed on the symbol and it is directly passed to the output. However, if PAPR exceeds the threshold, the algorithm is applied to that symbol until the PAPR is reduced below threshold. The proposed technique shows better reduction performance compared to the previously proposed techniques which combat the PAPR, such as clipping and filtering, Selective mapping, LDPC code. The findings of this work may be help in the designing of efficient and effective wireless communication with lower PAPR effect.