Improved Clipping Technique for Reducing the Peak to Average Power Ratio in OFDM Systems

Peak to Average Power Ratio (PAPR) is one of the disadvantages of OFDM system, which had been studied in several papers and reduced in several techniques. Clipping and filtering are an effective technique for reducing the PAPR in OFDM systems. It requires an accurate filtering to reduce the resulting in-band and out-ofband noise. In this paper, an improved clipping technique is proposed. The technique calculates the error signal between the original and clipped signals and then feeds it back to the data symbols input. The technique uses a weighting process to the error signal to minimize the effect of in-band distortion. Our technique aims to clip the OFDM symbol to some threshold that is calculated by assuming a clipping ratio of 1 and measuring the Root Mean Square value (RMS) of the signal. The result from the difference between the original and the clipped signal can be added to the frequency domain OFDM (input to the IFFT) with zero padding the high frequency subcarriers to reduce the side loops power (out-of-band radiation). This results in decreasing Adjacent Channel Interference (ACI) that may affect the neighboring systems. In addition, some weight is added to the inserted in-band signal to the desired data subcarriers to reduce the amount of interference and decrease the resulted BER. The PAPR is calculated for the time domain OFDM symbol using MATLAB/SIMULINK simulation which compares the proposed technique to the clipping and filtering technique. By using a weighting factor of 0.8, the proposed technique reduces the PAPR by more than 4dB with maintaining a good BER performance of 3.6x10-5 at SNR=9dB. Keywords— Clipping, Filtering, In-band distortion, OFDM, PAPR, Out-of-band radiation.