M.Sc. Alex Jäger
Technical University of Munich
Chair of Communications Engineering (Prof. Kramer)
Postal address
Postal:
Theresienstr. 90
80333 München
Biography
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.
Teaching
Nachrichtentechnik (ST 2024)
Machine Learning for Communications (WT 2023/24)
Digital Signal Processing for Optical Communication Systems (ST 2023)
Theses in Progress
Turbo Equalization for Optical Fiber and/or Phase Noise Channels with Memory
Description
Turbo equalization is an iterative approach to achieve a gain in terms of AIR compared to memoryless receivers for channels with memory. The student should read into the topic of Turbo equalization using, e.g., [1-2] or similar references and then search for applications for either optical channels, e.g., [3] or phase noise channels with memory, e.g. [4]
[1] https://ieeexplore.ieee.org/document/1267050
[2] https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1006557
[3] https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6595045
[4] https://ieeexplore.ieee.org/document/1504908
Supervisor:
Balanced Information Rates for Successive Interference Cancellation
Description
We are interested in developing SIC schemes that require only one code per stage.
Supervisor:
Constant Composition Distribution Matching
Description
The capacity-achieving input distribution of many channels, e.g., memoryless AWGN channels, is non-uniform. This motivates investigating constellations with arbitrary probability mass functions for data transmission. To map sequences of uniformly distributed bits to sequences of non-uniformly distributed symbols, distribution matchers (DM) are used. In particular, constant composition distribution matchers (CCDM) [1] enable fixed blocklength to fixed blocklength (f2f) mapping.
The seminar paper should provide a good overview of CCDM. This includes but is not limited to a comprehensible motivation for DM, a description of how DM embed into communication systems, a high-level overview of how CCDM works, and considerations regarding practical implementations, e.g., [1, Sec. IV].
The successful student will develop a profound understanding of DM and CCDM; see [2, Sec. 9.2], [3, Sec. 4.3], and references therein. Good literature research is an essential part of the task. The student is rewarded with a good understanding of an emerging research field in communications and a review of the foundations of modern communication systems.
The seminar paper may be extended to a research internship or master thesis afterward.
[1] P. Schulte and G. Böcherer, "Constant Composition Distribution Matching," in IEEE Transactions on Information Theory, vol. 62, no. 1, pp. 430-434, Jan. 2016.
[2] G. Böcherer, “Principles of Coded Modulation,” Habilitation thesis, Tech. Univ. Munich, Munich, Germany, 2018.
[3] P. Schulte, “Algorithms for distribution matching,” Ph.D. dissertation, Technische Universität München, May 2020.
Prerequisites
Profound knowledge of communication systems and information theory.
Supervisor:
Publications
2024
- Information rates of successive interference cancellation for optical fiber. IEEE J. Sel. Areas Commun., 2024 more… Full text ( DOI )
- Successive interference cancellation for optical fiber using discrete constellations. European Conference on Optical Communications (ECOC), 2024 more…
2023
- Bounding the Capacity of Fiber-Optic Channels. 20th Joint Workshop on Communications and Coding (JWCC), 2023 more…
2022
- Achievable Rates for Space-Division Multiplexed Optical Channels with Direct Detection. 6G-Life Project Work Package Workshop, 2022 more…