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Orthogonal frequency division multiplexing (OFDM) is one of the widely used modulation techniques for nonlinear communication systems. It offers high data rate, spectral efficiency, robustness to multi path fading, simple receiver design, etc. But, it suffers from high peak-to-average power ratio (PAPR) which causes inband signal distortion and out of band spectral regrowth and results in significant reduction in power efficiency when passed through a nonlinear power amplifier. In this paper, a simple method of PAPR reduction, clipping and filtering is investigated. Effects of clipping and filtering on the performance of OFDM signal such as power spectral density, PAPR, and bit-error rate has been investigated through Matlab simulations. The results obtained indicate that at clipping ratio, CR = 1.4 and 1% of CCDF the reduction in PAPR values are 8.8 dB and 5.4 dB for clipped only and both clipped & filtered signals, respectively. The clipping operation also causes degradation in the BER performance. At 10 dB of signal power and at CR = 1.4, BER values are 1.0 X 10 -2 for clipped signal, 5.1 X 10 -3 for both clipped & filtered signals and 7.8 X 10 -4 for unclipped signal. This increase in BER value is due to distortions caused during the process of clipping and filtering. Keywords-Orthogonal frequency division multiplexing, peak to average power ratio, clipping and filtering.I.

High Power Amplifier in wireless communication systems exhibit nonlinear behavior which causes signal degradation. This is detrimental to the signals that pass through it. It appears in the form of Harmonic distortion, Gain compression, Inter-modulation distortion, Phase distortion, adjacent channel interference, etc. Orthogonal frequencydivision multiplexing (OFDM) is considered to be better techniques for multicarrier wireless communication. It has tolerance to inter-symbol interference and good spectral efficiency but are subjected to nonlinearities of power amplifiers, due to their high peak-to-average power ratio (PAPR). In this paper, some of the basic PAPR reduction techniques like: Peak clipping, random phase shifting, selected mapping (SLM) and dummy sequence insertion (DSI) methods have been discussed. The results obtained has been compared with original PAPR which suggests improvement in nonlinearity with modest reduction in efficiency and increase in hardware implementations. Among the various techniques SLM method gives low PAPR than other methods.

<p>Highly linear power amplifiers are required for transferring   large amount of data for future communication. Orthogonal frequency division multiplexing (OFDM) provides high data rate transmission capability with robustness to radio channel impairments. It has been widely accepted for future communication for different services. But, it suffers from high value of peak-to-average power ratio (PAPR). High value of PAPR drives high power amplifier into its saturation region and causes it to operate in the nonlinear region.  In this paper, comparative study of four different PAPR reduction techniques: clipping and filtering (CF), selective mapping  method (SLM), partial transmit sequence (PTS) and DFT- spread technique  have been done. Mathematical modeling and Matlab simulations have been performed to arrive at the results with 4 QAM modulation format and 1024 number of sub carriers. At 0.01 % of complementary cumulative distribution function (CCDF) significant reduction of 11.3, 3.5, 3.4 and 1.0 dB have been obtained with DFT- spread, SLM, PTS and CF techniques respectively.</p>

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