Power amplifier effects on frequency localized 5G candidate waveforms

One important direction in advanced communication waveform studies for future wireless communications is improved spectrum localization, i.e., minimization of the power leakage outside very narrow guardbands around the useful signal band. This helps to improve the spectrum efficiency, especially in difficult radio access scenarios, like cognitive radio and dynamic spectrum access. In contrast to basic OFDM based waveforms, this allows dense frequency-division multiple access without need for precise synchronization of users. Various multicarrier and single-carrier waveforms with effective spectrum localization are available, but their spectral characteristics have so far been investigated mostly in the digital processing domain. For practical deployment, it is necessary to study the effects of practical transmitter power amplifiers (PAs) on the waveform characteristics, together with power amplifier linearization and peak-to-average power ratio (PAPR) reduction methods. This paper focuses on these issues, deriving PA backoff requirements using the soft envelope limiter model, corresponding to an ideally linearized PA, together with a generic PAPR reduction method based on windowed clipping. It is demonstrated that this method, when applied with well-linearized PA, helps to significantly reduce the required power amplifier backoff for both single-carrier and multicarrier waveforms, with the potential of reaching extremely low out-of-band radiation with realistic backoff values. The results are generally applicable to all spectrally localized waveforms.