Functions and Abstractions for Radio Access Network Softwarization

It is expected that future mobile Radio Access Networks (RANs) should offer enough degrees of freedom to be adapted quickly and, at low cost, to operate in ways that may be not conceived today. The possibility to program the network, to offer new and tailored services, will encourage a myriad of technical and business innovations. With this goal, several paradigms and network architectures that comprise RAN softwarization are being proposed. The research presented in this thesis contributes to softwarization for heterogeneous RANs. Joint development of functions and abstractions is addressed. A simplified framework for RAN softwarization is presented, consistent with the paradigms of Software Defined Networks (SDN), and other architectures proposed in the literature. The framework consists of a Central Coordinator and Controller (CCC) for logical centralized network management, plug-in Network Functions (NFs), or applications, and a RAN with Real Time Controllers (RTCs). We discuss the development, implementation and performance of two kinds of NFs. First, NFs for Inter-Cell Interference Coordination (ICIC), optimizing inter-tier resource allocation at cell and network-level, with muting in one or two tiers. Second, a NF for dynamic spectrum management in Frequency-Division Duplexing (FDD) Flexible Duplexing cells. In addition, local functions and abstractions for the RTCs are discussed. As examples, we present two methods for optimizing switching points in the context of Adaptive Modulation and Coding (AMC). As a basis for this, we discuss functions to abstract link-level details. Results from simulations with ICIC-NFs in different Heterogeneous Networks (HetNets), show that the proposed functions and abstractions are suitable to improve the performance of the network. For FDD flexible duplexing cells, the approach presented as a NF helps to determine the trade-off between downlink transmit power of a flexible duplexing cell, and distance between this cell and a victim, belonging to another operator. The functions and abstractions discussed for the RTCs, complete the framework. From the results observed, we can conclude that the adoption of a framework as the proposed, based on RAN softwarization, with suitable functions and abstractions, provides a promising solution to make the RAN flexible enough to incorporate new and tailored services.