Ergodic mutual information and its fluctuation in multi-level MIMO relay system

The help of relay devices is of paramount importance to overcome the impairments of channel randomness, especially in a rich scattering scenario with no line-of-sight communication path. Relaying strategies are gaining increasing attention due also to the eventual deployment of small-cells in future generations wireless networks, where short-range communication is inherently to be favored, to cope with path-loss and to jointly improve energy-efficiency of the links. MIMO is naturally combined with relaying in order to further increase the overall spatial degrees of freedom of the system. Since the early introduction of relay-aided transmission protocols, in the field of information theory lot of efforts has been devoted to the analytical characterization of the performance of such strategies, with a main focus on dual-hop, single relay systems. This work moves a step toward the characterization of multilevel MIMO relay channels, where data transmission takes place through an arbitrary number of hops. We leverage tools and results from the physics of disordered systems, and put them into the framework of finite-sized multiple-antenna systems.