05 Fakultät Informatik, Elektrotechnik und Informationstechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6

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Publication Type: search.filters.UBSTyp.Abschlussarbeit (Master)Subject: search.filters.subject.620

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    Digital pre-distortion of broadband communication links using open-loop architecture
    (2021) Wiewel, Florian
    The ever-increasing demand for higher data rates and lower latency in wireless communications ultimately forces the developers of the underlying systems to use broadband links with higher order modulation formats to meet this demand. The use of these modulation formats results in strict linearity requirements on the system. On top of that power, efficiency is also an important aspect, since it has an impact on the operational costs and ecological compatibility. In a typical macrocell for modern wireless communication systems, the power amplifier (PA) of the base station consumes about 60% of the overall power and it is also the PA, which typically exhibits the strongest nonlinear transfer characteristic in the system. Unfortunately, power efficiency and linearity represent conflicting requirements in PA design. As a result, a compromise between these two requirements has to be made. Usually, the PA is designed for high power efficiency and with moderate nonlinear transfer characteristics. To compensate for the nonlinearity in the PA a technique called digital pre-distortion (DPD) is applied, which estimates the nonlinearity in the PAs transfer characteristic and applies the corresponding inverse transfer function to the complex baseband input signal of the PA in the digital domain. In contrast to many of the DPD experiments found in literature, which are applied to signals with bandwidths in the range of tens of megahertz, the targeted linearization bandwidth in this work is 5 GHz. For this purpose an open-loop DPD architecture based on the Volterra theory of nonlinear systems specifically the p-th order inverse has been implemented in software and applied to different amplifiers including a waveguide E-band transmitter operating around 73 GHz. Up to a signal bandwidth of around 1 GHz significant improvements in terms of signal quality could be observed in the conducted experiments. For signals with higher bandwidths problems with signal integrity caused the DPD to fail. Finally, the various problems are analyzed and potential improvements for increasing the DPD performance for wideband signals are suggested.
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    A preCICE-FMI Runner to couple controller models to PDEs
    (2023) Willeke, Leonard
    Partitioned simulation or co-simulation allows to simulate complex systems by breaking them into smaller, independent subsystems. The Functional Mock-Up Interface FMI enables co-simulation by defining a framework for simulation models. Models adhering to the standard interface (FMUs) are executed and coupled by an importer. This framework approach works well for models based on ODEs and DAEs but reaches its limits for models based on PDEs. Such models require sophisticated, legacy software packages not compatible with the FMI standard. However, only PDE-based models are able to accurately simulate many physical aspects important in engineering like heat transfer or Fluid-Structure interactions. A possible solution to this problem is the open-source coupling library preCICE. preCICE couples PDE-based simulation programs in a black-box fashion to achieve partitioned multi-physics simulations. The coupling of the FMI standard to preCICE would allow the co-simulation of FMI models with the more than 20 simulation programs in the preCICE ecosystem. This thesis is focused on the development of a preCICE-FMI Runner software to couple FMUs with preCICE. The Runner serves as an importer to execute the FMU and steer the simulation. Additionally, it calls the preCICE library to communicate and coordinate with other solvers. The scope is not to develop a general Runner software, but to couple FMUs that contain control algorithms with PDE-based models as a first step. The software is written in Python and relies on the Python package FMPy as well as the preCICE Python bindings. Two test cases show the functionality of the preCICE-FMI Runner. The coupling of ODE-based models with FMUs matches the results of a pure Python implementation with an accuracy of 10 −4 . The coupling of a PDE-based model to a controller FMU proofs the working principle, although the results could not be tested against other implementations. The scope of the implemented abilities restricts the possible simulation scenarios, but does not prohibit a general use for coupling scenarios beyond control applications.