I received my B.Eng. degree from the University of Applied Sciences Konstanz (HTWG) in 2020, and subsequently obtained my M.Sc. degree from the Technical University of Munich (TUM) in 2022.
During my Masters thesis, I conducted research on the topic of achievable information rates for space-division multiplexed short-reach fiber-optic communication systems using direct-detection receivers, while staying with the Optical Networks Group (ONG) at University College London (UCL).
Research Interests
Due to the presence of Kerr nonlinearities, a closed-form expression for the input-output relation of the fiber-optic channel cannot be derived, rendering the channel capacity indeterminate. Digital signal processing techniques, such as digital back-propagation, have been proposed as a means of mitigating nonlinear and linear fiber effects.
However, in wavelength switched networks, where receivers are only able to access their specific channel of interest and not interfering channels, only intra-channel effects, such as self-phase modulation, can be mitigated. As a result, cross-phase modulation remains a significant source of distortion in the received signal.
The nonlinear distortions that remain are typically modeled as correlated phase noise and inter-symbol interference within the channel of interest. My research focuses on developing coding schemes and receivers capable of mitigating these distortions.
Receiver scatter plots of a 16-QAM transmission with interfering channels using QPSK (leftmost plot), 16-QAM (middle plot) and Gaussian modulation (rightmost plot). Especially in the rightmost plot, nonlinear phase noise is clearly visible.
Time-varying phase noise is of interest in many communication scenarios, including high-frequency wireless channels and coherent optical communications.
In [1], the authors introduce an iterative receiver for channels distorted by phase noise. They use strong correlations in the phase noise process for mitigation. A downside is the requirement for pilot insertion, effectively decreasing spectral efficiency.
Expectation propagation (EP) [2][3, Ch. 10, Sec. 10.7] has been recently used to enhance the receiver design, thereby mitigating the need for pilot insertion [4].
The task of this seminar paper is to
summarize the system model used in [1],[4],
analyze the approach, benefits, and drawbacks in [1],
explain the principles of EP, and
compare how EP modifies the receiver in [4] relative to [1].
A successful submission provides intuition for tasks 1-3 and a thorough analysis of the differences between [1] and [4] for task 4.
After you have successfully applied for the topic, we will hold a kick-off meeting to discuss all necessary details for the upcoming work. After that, the responsibility for the seminar paper is all on you. You can always contact me, ask questions, and request meetings, and I am happy to assist you along the way. However, I need you to be proactive.
I can provide comments on your work (e.g., the paper's outline and some paragraphs you have already written) at any time you need them and guide you as you prepare your paper and presentation. Regarding final drafts, I comment on one complete version of your paper. Ideally, this would mean that you do some work (literature research, the paper's outline, the body, the introduction, and the conclusion), and we discuss your results after every step. Ultimately, you provide me with one final draft, and I will comment on it. The draft must be handed in at least 10 days prior to the paper submission deadline. This method is more successful and instructive than writing a paper a few days before the deadline.
Beware that when I comment on your work, this is not the same as a correction. My comments are suggestions for improving the quality of the work, but I cannot spend the time searching for and correcting every mistake that exists or could be made (this would also not align with the seminar's purpose).
I expect solid research. There should be two significant references. Those are papers you know in detail and that majorly impact your work. Of course, they are always accompanied by supporting references.
Prerequisites
A good knowledge of the Sum-Product algorithm (SPA) and perhaps experience with Approximate Message Passing is helpful. This can be obtained in our lecture, "Machine Learning for Communications." Alternatively, [5] provides a good overview of the SPA.
Real-time Data Streaming Architecture for Automotive Testbench Traffic
Description
The project aims to design a software framework that optimizes the decoding and streaming of automotive Ethernet traffic in real time, applies filtering to reduce redundant data, and enables efficient storage and analysis in a cloud environment.
Supervisor:
Alex Jäger - (Technica Engineering GmbH)
Completed Theses
Supervisor:
Alex Jäger, Paolo Carniello
Supervisor:
Alex Jäger, Juan Diego Lentner Ibanez
Supervisor:
Alex Jäger
Supervisor:
Alex Jäger
Supervisor:
Alex Jäger, Daniel Plabst
Supervisor:
Alex Jäger
Supervisor:
Alex Jäger, Thomas Wiegart
Supervisor:
Alex Jäger
Publications
2025
Alex Jäger: On Low-Complexity Mitigation of Nonlinear Inter-Channel Distortions in Optical Networks. 43. Sitzung der ITG-Fachgruppe „Angewandte Informationstheorie“, 2025 more…
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Alex Jäger: On Mitigating Equalization-Enhanced Phase Noise. 21st Joint Workshop on Communications and Coding (JWCC), 2025 more…
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Jäger, A.; Kramer, G.: Information rates of successive interference cancellation for optical fiber. IEEE J. Sel. Areas Commun. 43 (5), 2025, 1484-1497 more…
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2024
Alex Jäger: Successive Interference Cancellation for Optical Fiber Using Discrete Constellations. 2024 Munich Workshop on Shannon Coding Techniques (MSCT), 2024 more…
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Jäger, A.: A Tutorial on Methods for Message Passing with Continuous Variables. ICE Summer Doctoral Seminar, 2024 more…
Jäger, A.: Challenges and Research Trends for Fiber-Optic Communication Systems. CoC Industry Day, 2024 more…
Jäger, A.; Kramer, G.: Successive Interference Cancellation for Optical Fiber Using Discrete Constellations. European School of Information Theory (ESIT), 2024 more…
Jäger, A.; Kramer, G.: Successive interference cancellation for optical fiber using discrete constellations. European Conference on Optical Communications (ECOC), 2024 more…
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2023
Jäger, A.: Bounding the Capacity of Fiber-Optic Channels. 20th Joint Workshop on Communications and Coding (JWCC), 2023 more…
2022
Jäger, A.: Achievable Rates for Space-Division Multiplexed Optical Channels with Direct Detection. 6G-Life Project Work Package Workshop, 2022 more…