Advanced radio resource management techniques in modern cellular systems

The fast increase in the population of mobile users inspires the rapid development of wireless communication technology. There are more than 1 billion mobile broadband subscriptions worldwide today, and this number is expected to grow to 5 billion by 2016. The rapidly increasing number of mobile subscriptions involves the exponential growth of mobile data traffic which is primarily dominated by smartphones, mobile PCs and tablets. These new trends in wireless communications also include high (peak and average) data rates and low latency expectations from the user point of view, as well as, high spectrum efficiency and low cost of ownership from the network operator’s perspective. The wireless mobile systems of today have to meet these stringent requirements. Since the radio resource is limited and very expensive, the efficient use of the radio spectrum is extremely important from the cost of service point of view. This goal is particularly challenging for systems that are power, bandwidth, and complexity limited. A reduction in cost and an increase in bit rates at the same time can be achieved, for example, by more efficient reuse of spectrum through improved radio resource management (RRM) functions and by the use of multiple transmitter and receiver antennas that can significantly increase channel capacity. Therefore, the efficient use of radio spectrum plays a key role in maximizing the utilization of the system. This dissertation presents possible solutions on how to increase spectral efficiency by means of improved channel quality through the use of radio resource management (i.e., power control, interference management and scheduling) techniques, and through the proper coordination of the RRM functions exploiting fast backhaul infrastructure in multi-cell environment. In the dissertation, I also show how to exploit the better channel quality to achieve higher capacity (e.g., use of spatial multiplexing and adaptive modulation) and how to share the radio resources among users to guarantee a certain level of fairness. Then, I propose possible ways on how to employ these methods in a real modern cellular network (e.g., in the 3GPP Long Term Evolution (LTE) system). Finally, I propose a solution to further improve the performance of cellular networks in terms of increased resource utilization, improved user throughput and extended battery lifetime of user equipments by enabling device-to-device (D2D) communications on top of a cellular infrastructure. D2D communication introduces a new degree-of-freedom for RRM algorithms in finding the best configuration of parameters, since they have to select between the direct (device-to-device) or the cellular (via the base station) mode of operations. I show that the application of joint power control and mode selection are key RRM functions to manage the new interference situations and realize the potential gains of D2D communications in future cellular networks. The results of this dissertation show that the proposed advanced RRM functions are essential means to achieve high spectral efficiency for cellular and D2D communication links in today’s and future multi-cell mobile systems.