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Frontend Impairments and Interference Compensation in FDM Systems
Harvánek, Michal ; Wang, Yide (oponent) ; Gazda,, Juraj (oponent) ; Maršálek, Roman (vedoucí práce)
The out-of-band (OOB) performance of advanced, filter-based multicarrier waveforms can easily be deteriorated by the nonlinearity of Power Amplifier (PA). One of the common ways to eliminate such signal quality degradation is a Digital PreDistortion (DPD) applied in the transmitter. The introductory part of the thesis presents the study of the impact of selected transceiver imperfections on the performance of DPD linearizers. Starting from the PA model identification based on the data captured using the low-cost Software Defined Radio (SDR) platform, we evaluate the performance in terms of OOB signal emissions at the PA output for the case of typical representatives of frequency-localized multicarrier signals. We highlight the fact that frontend imperfections can significantly affect the performance of predistorters. Interference between users in adjacent channels negatively affects the achievable throughput of mobile networks. The complexity of DPD implementation is sometimes a showstopper for its implementation in mobile terminals, and the OOB radiation generated by nonlinearity could result in serious problems. Thus, the core of the thesis deals with the receiver-side cancellation of interference caused by a nonlinear PA. The proposed interference cancellation method subtracts the OOB emissions from the received signal. In contrast to the state-of-the-art approaches, our method employs over-the-air estimation of PA model parameters together with a particular frequency domain filtering method that allows to generate the required training data. As an exemplary waveform, we use a Generalized Frequency Division Multiplex (GFDM), and we also evaluate the method on the SDR-based test-bed.
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