title: Model-Based Bayesian Inference, Learning, and Decision-Making with Applications in Communication Systems
Creators: name: Alt, Bastian
Publisher: name: UNSPECIFIED
Year: 2022

description: This dissertation discusses the mathematical modeling of dynamical systems under uncertainty, Bayesian inference and learning of the unknown quantities, such as the system’s state and its parameters, and computing optimal decisions within these models. Probabilistic dynamical models achieve substantial performance gains for decision-making. Their ability to predict the system state depending on the decisions enables efficient learning with small amounts of data, and therefore make guided optimal decisions possible. Multiple probabilistic models for dynamical state-space systems under discrete-time and continuous-time assumptions are presented. They provide the basis to compute Bayesian beliefs and optimal decisions under uncertainty. Numerical algorithms are developed, by starting with the exact system description and making principled approximations to arrive at tractable algorithms for both inference and learning, as well as decision-making. The developed methods are showcased on communication systems and other commonplace applications. The specific contributions to modeling, inference and decision-making are outlined in the following. The first contribution is an inference method for non-stationary point process data, which is common, for example, in queues within communication systems. A hierarchical Bayesian non-parametric model with a gamma-distributional assumption on the holding times of the process serves as a basis. For inference, a computationally tractable method based on a Markov chain Monte Carlo sampler is derived and subsequently validated under the modeling assumption using synthetic data and in a real-data scenario. The second contribution is a fast algorithm for adapting bitrates in video streaming. This is achieved by a new algorithm for adaptive bitrate video streaming that uses a sparse Bayesian linear model for a quality-of-experience score. The algorithm uses a tractable inference scheme to extract relevant features from network data and builds on a contextual bandit strategy for decision making. The algorithm is validated numerically and an implementation and evaluation in a named data networking scenario is given. The third contribution is a novel method that exploits correlations in decision-making problems. Underlying model parameters can be inferred very data-efficiently, by building a Bayesian model for correlated count data from Markov decision processes. To overcome intractabilities arising in exact Bayesian inference, a tractable variational inference algorithm is presented exploiting an augmentation scheme. The method is extensively evaluated in various decision-making scenarios, such as, reinforcement learning in a queueing system. The final contribution is concerned with simultaneous state inference and decision-making in continuous-time partially observed environments. A new model for discrete state and action space systems is presented and the corresponding equations for exact Bayesian inference are discussed. The optimality conditions for decision-making are derived. Two tractable numerical schemes are presented, which exploit function approximators to learn the solution in the belief space. Applicability of the method is shown on several examples, including a scheduling algorithm under partial observability.