Statistical Analysis of Hardware Impairments in Communication Systems

Doktorsavhandling, 2023

This thesis delves into the study of hardware impairments, the inevitable limiting factors in radio frequency (RF) communication systems, and their substantial influence on system performance. It addresses the incongruity between the often stringent requirements imposed by standards and the innate imperfections of analog circuits present in real-world RF electronics. Key hardware impairments, namely In-phase and Quadrature-phase Imbalance (IQI), phase noise, power amplifier (PA) nonlinearities, and antenna array perturbations, are studied, offering comprehensive overviews of their individual characteristics and their interactions with each other.

The thesis also focuses on the effects of PA nonlinearity on widely used signal transmission optimizations, namely pulse shaping and matched filtering techniques. The nonlinear behavior of the PA, which can lead to signal distortions and inter-symbol interference, is shown to impact these techniques, posing considerable challenges to reliable communication. Moreover, a noticeable gap exists in the academic literature concerning an accurate analysis of the effect of PA nonlinearity on pulse shaping and matched filters. Such a gap underscores the need for a rigorous investigation into how these transmission optimizations are influenced by the PA's nonlinearity. As the first contribution of this thesis to the literature, in Paper A, a detailed study is conducted to comprehensively address these effects, bridging the existing knowledge gap and providing new insights into the interplay between PA nonlinearity, pulse shaping, and matched filter.

As a complementary study to Paper A, Paper B delves deeper into the intricacies of PA nonlinearity, examining the impact of various waveforms and modulation orders. Within this exploration, a waveform factor is formulated, elucidating the interplay between waveform statistics, amplifier-specific parameters, and signal power in determining the total distortion power. Furthermore, a theoretical closed form for the nonlinear distortion, both in-band and out-of-band, is derived. This derivation reveals a notable finding: the distortion approximately distributes evenly between the in-band and out-of-band portions of the spectrum, offering a nuanced understanding of how PA nonlinearity manifests across adjacent frequencies.

Moreover, in paper C, the effects of IQI and phase noise, in conjunction with PA nonlinearity, are analyzed, which can lead to a scrambled effect that further degrades the received signal quality. An additive noise modeling technique is introduced as a novel approach to effectively represent these combined effects. This technique facilitates accurate tracking of system performance under varying hardware impairment conditions, serving as a valuable tool to understand the collective impact on the system and develop mitigation strategies.

The thesis further contributes to the field by providing statistical models for beam pattern variations due to antenna array perturbations in Paper D. The perturbations are random variations in phase, gain, and antenna element positions. These models enable an accurate projection of system performance under various conditions, helping to bridge the gap between theoretical design and practical implementation in RF communication systems.

This comprehensive investigation of hardware impairments in communication systems paves the way for more resilient design strategies, enhancing the robustness and reliability of future RF communication systems.