Optimized Spectrum Constrained Crest Factor Reduction Technique Using Polynomials

Abstract

This paper proposes a new peak-to-average power ratio (PAPR) reduction technique using a polynomial soft clipping function identified through a nonlinear constrained optimization. The power efficiency optimization problem of a linearized power amplifier can be considered as the minimization of the PAPR constrained by meeting the spectral mask requirements of the signal standard. It is demonstrated that the proposed approach can reduce the PAPR from 9.9 dB to 5.5 dB while meeting the spectral mask of the WCDMA standard. To compare the results with the traditional clipping and filtering method, the 5.5 dB PAPR clipped signal using the clipping and filtering technique was compared with the soft clipped signal. With the same efficiency, the error vector magnitude (EVM) for the soft clipped signal improved from 4.5% to 1.3% using post-compensation. Later, clipping and filtering is combined with the soft clipping technique. It is shown that the combined structure can reduce the PAPR to 3.4 dB, while passing the adjacent channel power ratio and EVM requirements. The performance of the proposed method in the presence of AWGN and fading channels has been evaluated for 64QAM modulations using OFDM modulated symbols.

Active Constellation Modification Technique for PAPR Reduction of OFDM Signals

“…The CAF approaches presented in [8]- [13] utilize OFDM signal hard clipping techniques to reduce PAPR and use OOB and IB handling algorithms to mitigate OOB emission and IB distortion, respectively. Processing for the IB and OOB can be performed on either the clipping noise, as studied in [8], [11]- [13] or the clipped OFDM signal, as discussed in [9], [10]. Rather than utilizing the clipped OFDM signal, the methods presented in [8], [11]- [13] employ the clipping noise in their analysis and convert it into an equivalent form, similar to the method described in [9], [10].…”

“…Processing for the IB and OOB can be performed on either the clipping noise, as studied in [8], [11]- [13] or the clipped OFDM signal, as discussed in [9], [10]. Rather than utilizing the clipped OFDM signal, the methods presented in [8], [11]- [13] employ the clipping noise in their analysis and convert it into an equivalent form, similar to the method described in [9], [10]. Fig.…”

“…Recently, improved methods of CAF to reduce processing delay and computational complexity, increase PAPR reduction efficiency, and improve BER performance have been continuously proposed. The constrained clipping methods in [10]- [13] maintain both IB deformation and OOB emission at suitable levels to simultaneously meet the requirements of spectral mask and BER performance while ensuring the desired PAPR level of reduction without any iteration. Therefore, they achieve a processing delay reduction and a better balance between OOB radiation and IB distortion.…”