Papr reduction using soft clipping and ACI rejection in OFDM system

OFDM(orthogonal frequency division multiplexing) is usefully applied for the DAB (digital audio broadcasting) and DVB(digital video broadcasting) system due to the high spectral efficiency and the robustness to the ISI (intersymbol interference) and multipath fading. However, the OFDM signal has a large PAPR (peak to average power ratio), which results in the significant nonlinear distortion when it passes through a HPA(high power amplifier) such as TWTA(traveling wave tube amplifier) and SSPA(solid state power amplifier). We propose a new PAPR reduction method using soft clipping and filtering. Unlike the conventional hard clipping, soft clipping has non-zero slope in the clip region. Next, filtering which uses the additional FFT and IFFT transform processes is applied in order to reject the out-of-band clip noise. Although the filtering removes the out-of-band noise, it oppositely increases PAPR in small quantity. Since HPA (high power amplifier) increases the power consumption according to the linearity range, soft clipping for SSPA lowers the power consumption and is more efficient than the conventional hard clipping method. By the results of proposed method, the wanted PAPR can be obtained and there is no out-of-band radiation caused by clipping process.