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Promotionsprüfung von Dr.-Ing. Tim Schmitz
Dr.-Ing. Tim Schmitz hat seine mündliche Promotionsprüfung am 17. Dezember 2019 erfolgreich abgeschlossen. Bereits am Freitag, 13. Dezember 2019 berichtete Dr. Schmitz in einem 45-minütigen Vortrag über seine Arbeiten zum Thema:
"Continuous-Amplitude Error Protection of Discrete-Time Signals"
Abstract: Transmitting analog audio, video or sensor data with a digital system requires sampling and quantization. While a sampled signal can be reconstructed perfectly if the Nyquist-Shannon sampling theorem is met, quantization unavoidably abbs irreversible errors. Given a certain bitrate for quantization (or source coding in general), the achievable signal quality is therefore limited. Transmission of the signal over a noisy channel causes additional errors. If some part of the bitrate is used for protecting the signal with a channel code, these additional errors can be reduced or even eliminated. However, this reduces the achievable maximum quality of the gross bitrate is fixed. Since this compromise between quantization and channel coding is often designed for the worst-case channel, the signal quality saturates early with increasing channel quality, and transmission over a better channel is far below optimum. Instead of conventional digital systems, this thesis covers a continuous-amplitude, discrete-time system. Such a system does not exhibit this saturation of the signal quality, as its performance further improves with increasing channel quality. An example of such a system is a channel coding strategy using analog modulo block codes (AMB codes) for error protection. The encoder multiplies the unquantized symbol vector with a code matrix and limits the transmission power with a modulo operation. In practice, AMB coding is implemented by digital signal processing. The digital representation of the information symbols can be very precise and no coarse quantization is required for bitrate reduction.