Emil Björnson - Communication systems
Date: September 19th 2013 Location: Eurecom - Eurecom
The use of multiple antennas at base stations is a key component in the design of cellular communication systems that can meet high capacity demands. The downlink transmission from base stations to users is particularly limiting, both from a theoretical and a practical perspective. The performance of these multi-cell systems depends on how the available time, power, frequency, and spatial resources are divided among the users, which is known as resource allocation. The interdependence between these design parameters and the system performance is complicated, but the throughput, user satisfaction, and revenue can be greatly improved if we understand the nature of resource allocation and how to optimize it for high spectral efficiency. Resource allocation is naturally formulated as a multi-objective optimization problem. This formulation reveals the inherent difficulties: (a) the overwhelming spatial degrees-of-freedom created by the multitude of transmit antennas; and (b) the fundamental tradeoff between maximizing aggregate system throughput and maintaining user fairness. To find a suitable resource allocation solution we therefore need to select a subjective system utility, which can be anything between maximizing the aggregate throughput to giving all users the same throughput. This talk will show that the choice of system utility has a large impact on the solvability. The selection is therefore as important as the actual optimization of the selected metric. A pragmatic approach is proposed where the system utility is chosen to enable practically feasible signal processing solutions. The talk will also convey some insights on the underlying problem structure that have been acquired over the last decade. This talk essentially provides an outline and summary of a research book with the same title, written by Emil Björnson and Eduard Jorswieck. It was published in Foundations and Trends in Communications and Information Theory in January 2013. This book provides the fundamentals of resource allocation in multi-cell multi-antenna scenarios, along with recent advances in signal processing that enable robustness to channel uncertainty, distributed optimization, and adaptation to transceiver hardware impairments. The important connections to the seemingly different areas of cognitive radio, multi-casting, and physical layer security are also described.