# Autonomic Network Management and Cross-Layer Optimization in Software Defined Radio Environments
## 3 Autonomic Framework for Network Management and Cross-Layer Optimization in SDR
### Cross-Layer Optimization  
The proposed framework focuses on the three lower layers of the protocol stack, namely the Physical (PHY), Medium Access Control (MAC) and Network (NET) layers, which are extended to include a vertical cross-layer interconnection. The entire stack is realized individually in each MN. More precisely, the physical layer is enhanced with SDR features such as spectrum sensing. The cross-layer functionality related with the involved entities and the respective ACL are presented in Figure 4.  
Complying with the SDN concept, the proposed framework allows the decoupling of the control and data plane, where the latter implements only the data forwarding related operations and does not perform any type of control. As far as non-control functionalities are concerned, the three layers remain essentially unaltered compared to the traditional protocol stack. Specifically, the data plane of each MN (i.e., SU) is responsible for providing the ambient information of each individual layer to build the self- and environment-awareness, through the Information Collection component. This cross-layer information from the data plane includes information about the gains of the wireless channels (PHY), the interference among the communication links (MAC) and various network parameters such as queue lengths or the number of active traffic flows (NET).  
Contrary to the data plane, the control plane is responsible for the Decision Making component, performing the Resource Channel Allocation (RCA). The control plane utilizes the information collected by the Information Collection component and then decides the execution of the respective action, implemented by the Execution component, returning feedback to the three layers (i.e., transmission channels, power level, etc.). In particular, the control plane of each MN, through the SDN controller interface, interacts with the control plane of the SDN controller via exchanging signaling messages. Accordingly, the SDN controller is responsible to arrange virtual resources to compute the VUF  
Figure 4: Generic ANMO-SDR functionality.  
related with the selection of the most efficient channel allocation, as requested by each MN. Subsequently, the VM sends through the SDN-controller the relevant computation instance of the VUF to the requesting MN, enabling it to assign available channels according to its desired operational requirements. The chosen channel by each SU is communicated to the neighboring SUs, which update their status and sequentially proceed to the VUF computation, as a recurring process. The decision making is further enhanced by the SDN controller, which enforces global policies (i.e., \"globally minimize collisions\", or enforcing a faster \"best effort\" channel allocation) regarding resource allocation for all three layers.  
In summary, the objectives of the proposed architecture include reconfiguration flexibility, efficient use of the bandwidth, as well as, efficient and transparent D2D communications, without interrupting the primary network operation. The detailed analysis of the implementation of the proposed architecture in CRNs is introduced in the following section, where the aforementioned objectives of the proposed architecture are translated to specific performance metrics.