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. Relay- ing 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 proto- cols, 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-stage systems. This work moves a step toward the characterization of multi-level MIMO relay channels, where data trans- mission takes place through an arbitrary number of hops. We leverage tools and results from the physics of disordered systems, and put them into the frame- work of finite-sized multiple-antenna systems.