Evaluation of digital linearization techniques for PAs under 5G waveform operation in spectrum sharing scenarios

This project has been oriented to improve the efficiency and the linearization of power amplifiers (PA) with the combination of crest factor reduction (CFR) techniques and digital predistortion techniques (DPD). These techniques have been applied to Filter Bank Multi Carrier (FBMC) signals, which is one of the candidate modulations for future 5G systems. Since these signals are composed by a multicarrier modulation, they show a high Peak to Average Power Ratio (PAPR), that drive the RF amplifiers into saturation and thus cause distortion unless operation under excessive back-off is followed. The PAs are inefficient when they are operated far from the compression point (i.e. with a large back-off). These amplifiers are non-linear systems that add distortion to the signal. For this reason, we have employed the CFR techniques and DPD techniques to guarantee the linearization-efficiency trade off being required, thanks to the clipping of the signal peaks that cause non-linearities and the inversion of the non-linear response of the PA, that allow increasing the average power operation of the power amplifier. To validate the effectivity of these techniques, some simulation work has been conducted in Matlab and then the concepts have been evaluated in a real hardware environment. The results have show that these techniques can improve the communication systems of a base station (BS), given the fact that typical figures of merit such as the EVM or the ACPR of a base station transmitter that were not fulfilling the standard requirements, become significantly improved and fully compliant after applying the techniques. For FBMC signals with holes created to allocate LTE signals (primary system) in scenarios of spectral coexistence, we have also demonstrated the improvement of the primary system immunity to FBMC interference thanks to the digital linearization techniques (due to the enhanced Signal to Interference plus Noise Ratio or SINR increase)