On interference management techniques for efficient multi-user communications

Abstract

In this thesis, we develop and analyze interference management techniques for efficient multi-user communications. We investigate how to suppress multi-user interferences effectively. Specifically, we consider interference management techniques using transmit and/or receiver beamforming to optimize our communication systems in the sense of multiplexing gain [1] or arbitrary weighted sum-rate. In the first chapter, the multiplexing gain of $\It{K}$-user interference channel with partially connected interfering links is analyzed. The motivation for the partially connected links comes from the fact that not all interferences are equally strong in practice. The multiplexing gain is characterized as a function of the number ($\It{K}$) of users and the number ($\It{N} \ge 1$) of interfering links. Our analysis is mainly based on the interference alignment (IA) technique to mitigate interference. Our main results are as follows: One may expect that higher multiplexing gain can be attained when some of interfering links do not exist. However, when $\It{N}$ is odd and $\It{K}$=$\It{N}$+2, the multiplexing gain is not increased beyond the optimal multiplexing gain of fully connected interference channel, which is $\frac{\It{KM}}{2}$ with $\It{M}$ number of antennas. The number of interfering links has no influence on the achievable multiplexing gain using IA, but affects the efficiency in terms of the number of required channel realizations: When $\It{N}$=1 or 2, the optimal multiplexing gain of the fully connected interference channel is achievable with a finite number of channel realizations. In case of $\It{N} \ge 3$, however, the multiplexing gain of $\frac{\It{KM}}{2}$ can be achieved asymptotically as the number of channel realizations tends to infinity. In the second chapter, an efficient IA scheme is developed for $\It{K}$-user single-input single -output frequency selective fading interference channels. The main idea is to steer the transmit beamforming matr...