Interference-Limited Communication Systems

Inter-user interference is one of the most important challenges in modern communication systems since a dense reuse of resources is required due to the scarcity of the available spectrum. For instance, interference can occur if several independent links use a shared medium (interference channel), if a base station simultaneously transmits to multiple users (broadcast channel), or if no full decoding is performed at the relay in a relay-aided transmission (e.g., relay channel with partial decode and forward).

In all these situations, a better system performance can be achieved if the interference between the concurrent transmission is coordinated or even compensated by means of coding or signal processing. However, to this end it is necessary to jointly optimize the transmit strategies of the various communication links. Unlike in systems without interference, this often leads to nonconvex optimization problems, whose globally optimal solutions can usually not be obtained in a computationally efficient manner. In addition, it turns out that conventional paradigms about optimal transmit strategies are not necessarily true in systems with a significant amount of inter-user interference. For instance, separate coding on each carrier as well as the use of so-called proper Gaussian input signals may no longer be optimal in such systems, even though they optimize the achievable rates in the interference-free case.

Our research interests lie both in understanding fundamental limitations on the performance of interference-limited communication systems and in developing dedicated low-complexity optimization algorithms for designing close-to-optimum transceivers in such system. For instance, one of our research projects studies the interplay between underlay device-to-device links and a cellular network operating in the same frequency range. Another part of our research is to study performance gains that can be achieved in interference-limited communication systems by making use of new transmit paradigms such as improper signaling or coding across carriers.