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 to 5.5 dB while meeting the spectral mask of the wideband code-division multiple-access 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 are 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 additive white Gaussian noise and fading channels has been evaluated for 64QAM modulations using orthogonal frequency-division multiplexing modulated symbols.