On Spectral Efficiency of OFDM Signals Based on Windowing

We discuss the spectral efficiency of orthogonal frequency -division multiplexing (OFDM) signals widely adopted in practical systems from a viewpoint of their power spectral density property. Since the con-ventional OFDM does not make use of pulse shaping filter, its out-of -band (OOB) spectrum may not be negligible especially when the number of subcarriers is small. Thus, in practice, windowing is applied to mitigate OOB emission by smoothing the transition of consecutive OFDM symbols, but its effectiveness has not been well investigated. Furthermore, OFDM signal suffers from nonlinear distortion associated with its high signal peak -to-average power ratio (PAPR), which also leads to OOB radiation. We examine how power amplifier nonlinearity affects the spectral efficiency based on the theoretical results developed in the literature.