The effectiveness of signal clipping for PAPR and total degradation reduction in OFDM systems

Abstract

Signal clipping has been suggested as an effective peak-to-average power ratio (PAPR) reduction scheme for orthogonal frequency-division multiplexing (OFDM). This paper analyzes clipped M-ary differentially encoded phase-shift keying (M-DPSK) OFDM. The impact of input power backoff (IBO) of a nonlinear power amplifier (PA) is evaluated. An effective PAPR reduction scheme should provide one of the two equivalent enhancements: 1) a reduced error floor at a given backoff, or 2) a reduced required IBO to achieve a target BER. The later is addressed by determining the total degradation (TD) of the system at various IBO. By this measure, it is shown that clipping is ineffective. Moreover, it is shown that clipping PAPR reduction doesn't improve the spectral broadening caused by the PA. The linearity of the amplifier is viewed at various backoff ratios, defined as K = IBO/PAPR. Since K is best viewed statistically, so is the linearity of the PA. As a side note, the formula suggested by A. J. Cann (1980) is shown to be equivalent to the often referenced Rapp solid-state PA model