# Autonomic Network Management and Cross-Layer Optimization in Software Defined Radio Environments
## 2 State of the Art and Background Information  
### Programmable Networks and Network Virtualization  
Innovative concepts, such as network virtualization, SDR, and SDN, promote the design of more advanced and flexible network architectures [5]. The aforementioned technologies have already been developed individually and have been applied to different layers of the protocol stack, however, the convergence of these overlying and complementary technologies can further expand the amount of programmability on the network and support different innovative applications [1]. More precisely, a programmable (software-based) network architecture implements the various layers of the protocol stack in software, enabling on the fly changes without interruption of the network operation [6]. Specifically, SDN promotes the abstraction of the network logic from hardware implementation into software, proposing the separation of the data and control planes, and introducing a network controller to coordinate the network's operations. The programmable control plane concerns the softwarization of the functions that control the network behavior, including for example routing protocols and network configuration [7]. Accordingly, programmability in the data plane can be implemented using SDR [8]. SDR technology signifies the shift from static and fixed radio hardware devices towards the total programmability of layer-1 functions, such as the operating frequency, system bandwidth, modulation, and source encoding. An essential application domain of SDR is to enable more efficient spectrum utilization through opportunistic use of the spectrum [5]. Ultimately, bridging SDR and SDN will make it possible to bring the softwarization and virtualization of wireless networks down to the physical layer, which will unlock the full potential of next generation networks [8; 9]. In a similar direction, network virtualization can logically separate a single physical network infrastructure into multiple logical virtual networks, enabling customized support of application-specific services [6], and can lead to more efficient utilization of resources, presenting benefits in terms of security, cost reduction, energy efficiency, and efficiency of operations (reliability and scalability) [5]. The European Telecommunications Standards Institute (ETSI) is currently standardizing a set of primitives and requirements for network virtualization on a standard known as NFV. NFV can beneficially be combined with SDN and SDR mechanisms [9], by providing the infrastructure upon which the SDN and SDR software can be executed [5]. SDN and SDR in combination with NFV can virtualize the radio and the network infrastructure into separate and independent infrastructures, referred to as network slicing or vertical slicing [9], enabling the inclusion of the most appropriate protocols and mechanisms to deal with each traffic class [5]. Each network/radio slice is typically deployed as one or more NFV instances [10]. Current research directions on virtualization, promote the implementation of network entities as Virtual Machines (VMs), focusing mainly on control plane entities, which can be achieved without major changes to the current Evolved Packet Core (EPC) deployment [11]. Related approaches implementing SDN in 5G networks include [12; 13; 14; 15] among others, which introduced a programmable controller to allow the separation of control and data plane, while also in [12; 14], core control functions were arranged to the cloud for reliability and scalability. In addition, [16] moved the logical centralized control closer to the edge in mobile networks, utilizing fog computing for control at the Radio Access Network (RAN) level, in order to serve densely deployed cells; while cloud computing was used for control in the core network for packet processing and forwarding, leading to an end-to-end SDN solution for mobile networks [17].