PhD defence by Shajeel Iqbal

Title: Advanced Polar-Coded Modulation Techniques for Next-Generation Optical Communication Systems


Principal supervisor: Prof. Søren Forchhammer
Co-supervisor: Assoc. Prof. Darko Zibar
Co-supervisor: Prof. Leif Katsuo Oxenløwe
Co-supervisor: Dr. Metodi Yankov

Evaluation Board
Prof. Karsten Rottwitt, DTU Fotonik
Assoc. Prof. Qi Zhang, Department of Engineering, Aarhus University, Denmark
Dr Georg Böcherer, Huawei Technologies, Paris, France


Master of the Ceremony
Assoc. Prof. Michael Galili


The increasing demand for bandwidth-intensive internet services has pushed researchers to find methods which can help in increasing the spectral efficiency (SE) of the optical networks. At the same time, energy-efficient solutions are sought after more than ever. To meet the requirements of next-generation coherent optical communication systems, highly spectral efficient, reliable, flexible, and energy-efficient solutions for digital coded modulation (CM) systems need to be developed.

In this context, the contributions presented in this thesis relate to increasing the SE of the modern CM systems while incorporating energy-efficient

solutions such as constellation shaping (CS) techniques. Specifically, we study the use of a newly invented powerful forward error correction (FEC)

coding technique, known as polar coding, for optical communication systems.

We develop a flexible rate-adaptive CM system with polar codes by the combination with probabilistic constellation shaping (PCS) methods.

We then optimize this system by controlling a fraction of the bits in the frozen set of polar codes. A novel bit-interleaved coded modulation (BICM) system with pre-set bits and polar codes is then proposed. This results in increased energy and/or spectral efficiency for both linear and non-linear channels, or alternatively, increased maximum reach of the optical link at fixed spectral efficiency. The addition of pre-set bits, only slightly increases the complexity of the system. The system design provides a reliable, flexible, and energy-efficient solution to meet the demands of next-generation optical systems. The proposed system is independent of the underlying FEC code and can be directly extended to achieve higher baud rates and higher order modulation formats. Thus, it is attractive for future CM systems.

This thesis also investigates the potential use of polar codes to combat nonlinearities in the optical fibers. Polar codes are integrated with available

iterative non-linear compensation (NLC) techniques and are shown to be robust by numerical simulation results.

The main contribution of this Ph.D. project is to investigate the potential use of polar codes for the coherent optical systems, and to provide rate-adaptive

polar codes with probabilistic shaping, thus providing low-complexity solutions for flexible and energy-efficient polar-coded modulation systems.


fre 22 nov 19
13:30 - 16:30


DTU Fotonik



DTU Lyngby
Building 341, Aud. 23