Picture of Alex Jäger

M.Sc. Alex Jäger

Technical University of Munich

Chair of Communications Engineering (Prof. Kramer)

Postal address

Theresienstr. 90
80333 München


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.

Available Theses

Theses in Progress

Constant Composition Distribution Matching


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.


Profound knowledge of communication systems and information theory.


Alex Jäger



  • Jäger, A.; Kramer, G.: Information rates of successive interference cancellation for optical fiber. IEEE J. Sel. Areas Commun., 2024 more…


  • Alex Jäger: Bounding the Capacity of Fiber-Optic Channels. 20th Joint Workshop on Communications and Coding (JWCC), 2023 more…


  • Alex Jäger: Achievable Rates for Space-Division Multiplexed Optical Channels with Direct Detection. 6G-Life Project Work Package Workshop, 2022 more…