Biography

Christian Deppe received the Dipl.-Math. degree in mathematics from the Universität Bielefeld, Bielefeld, Germany, in 1996, and the Dr.-Math. degree in mathematics from the Universität Bielefeld, Bielefeld, Germany, in 1998. He was a Research and Teaching Assistant with the Fakultät für Mathematik, Universität Bielefeld, from 1998 to 2010. From 2011 to 2013 he was project leader of the project ``Sicherheit und Robustheit des Quanten-Repeaters´´ of the Federal Ministry of Education and Research at Fakultät für Mathematik, Universität Bielefeld. In 2014 he was supported by a DFG project at the Institute of Theoretical Information Technology, Technische Universität München. In 2015 he had a temporary professorship at the Fakultät für Mathematik und Informatik, Friedrich-Schiller Universität Jena. Since 2018 he is at the Department of Communications Engineering at the Technical University of Munich. He is project leader of several projects funded by the BMBF, the DFG and the state of Bavaria.

Teaching

• SS 2014 Lecture: Data transmission with feedback
• WS 2014/2015 Lecture: Quantum Information Theory
• SS 2015 Lecture: Computability and Complexity
• SS 2015 Lecture: Information Theory
• SS 2015 Lecture: Numerical Mathematics - Supplements
• WS 2015/2016 Lecture: Quantum Information Theory
• SS 2016 Lecture: Quantum Information Theory
• WS 2016/2017 Lecture: Quantum Information Theory
• SS 2018 Lecture: Multi User Information Theory
• WS 2018/2019 Lecture: Nachrichtentechnik II
• SS 2019 Lecture: Multi User Information Theory
• SS 2019 Lecture: Nachrichtensysteme - Kommunikationssysteme (LB)
• SS 2019 Lecture: Algorithms in Quantum Theory (together with Roberto Ferrara)
• WS 2019/2020 Lecture: Nachrichtentechnik II
• WS 2019/2020 Lecture: Information Theory (together with Gerhard Kramer)

Research

Secrecy Capacity of Classical - Quantum Channels

Investigation into communication via quantum channels started in the 1960s. Quantum mechanics differs significantly from classical mechanics, it has its own laws. Quantum information theory unifies information theory with quantum mechanic, generalizing classical information theory to the quantum world.

A quantum channel can transmit both classical and quantuminformation. We consider the capacity of quantum channels carrying classical information. This is equivalent toconsidering the capacity of classical-quantum channels, where the classical-quantum channels are quantum channels whose sender’s inputs are classical variables. We determine the secrecy capacity of the several channel with (quantum) wiretapper.

 

Message Transmission under Jamming Attacks

Our goal is to investigate in communication that takes place over a channel which is, in addition to the noise, subjected to the action of a jammer which actively manipulates the channel. A channel with a jammer is called an arbitrarily varying channel, where the jammer may change his input in every channel use and is not restricted to use a repetitive probabilistic strategy. In the model of an arbitrarily varying channel, we consider a channel which is not stationary and can change with every use. We interpret this as an attack of a jammer. It works as follows: the sender and the receiver have to select their coding scheme first. After that the jammer makes his choice to sabotage the message transmission. However, due to the physical properties, we assume that the jammer’s changes only take place in a known set. We consider classical and classical-quantum channels with a jammer and determine the (secrecy) capacity.

 

Identification over Channels

The implementation of this communication in today’s systems mostly based on the communication theory of Shannon. In this communication model, it is always assumed that the receiver’s goal is to decode all messages. Due to this strong goal, the coding scheme is inefficient for some cases. Ahlswede and Dueck have shown that there are more efficient solutions when the recipient’s goal changes. Instead of the decoder wanting to decode the message, he is only interested in whether a specific message has been sent. However, the sender does not know which message is interesting for the receiver. This communication task is called identification. We consider classical and classical-quantum channels with a jammer and determine the (secrecy) identification capacity.

 

Error-Correcting Codes with Feedback

We consider the problem of transmitting messages over a noisy channel with noiseless feedback. A sender wants to transmit a message over a noisy binary channel. We have a passive feedback, that means that the sender always knows what has been received. The i-th code letter depends on the message we want to transmit and the (i-1) symbols which have been received before. We suppose that the noise does not change more than a fixed number of symbols of a codeword. We consider several channel models with partial feedback and limited magnitude and construct coding strategies. Furthermore, we determine the capacity error function for these channels.