# Autonomic Network Management and Cross-Layer Optimization in Software Defined Radio Environments
## 5 Experimental Results  
The purpose of this section is to demonstrate the results of the implementation of the resource channel allocation algorithm, which was explained in detail in Section 4. We will provide specific quantitative results and show that our algorithm satisfies the required objectives by means of the metrics listed in Section 4.3, because it is an important element of the proposed hybrid architecture. The feasibility and the effectiveness of the aforementioned autonomic, cross-layer, MRF-based resource control mechanism for CRNs is demonstrated and quantitatively evaluated in realistic conditions by exploiting the capabilities of the ORCA project infrastructure. More specifically, the step-by-step implementation of the proposed approach is performed as follows: The real-world SDR devices (i.e., the SUs) perform cooperative spectrum sensing to provide the necessary environmental awareness and ambient information needed for the proper execution of the RCA algorithm. This information passes through the SDN controller to the dedicated VMs for each MN, which compute the VUF related with the proposed RCA algorithm (including energy function computation and Gibbs sampling). Accordingly, the VMs inform the MNs about their assigned channels, once again through the controller as it is shown in Figures 3 and 4. The MNs proceed to VUF computation sequentially, as a recurring process (i.e., sweep-based), informing each other for the selected channels during the channel allocation process, until all MNs allocate a suitable channel. According to the best of our knowledge, this is the first attempt to test in a real-world testbed a SDN/SDR-based D2D approach. The ORCA federation offers experimental facilities, with SDR devices incorporating relevant software and hardware building blocks that allow easy design, implementation and programming, while also achieving low runtime delay allowing end-to-end networking experimentation [4]. This infrastructure is a suitable testbed environment for setting up, evaluating and analyzing for the first time in real topologies and under realistic conditions the practical and operational aspects of the proposed resource management of secondary users of an SDR-enabled CRN with regard to variations of the wireless environment and the network (i.e., primary user activity). In particular, we employed IRIS (the reconfigurable radio testbed at Trinity College Dublin) and ORBIT (Open-Access Research Testbed for Next-Generation Wireless Networks) utilizing their facilities to study the impact of primary network users on secondary SDR-based CRNs and the effect of physical layer parameters of SDR devices on the MRF framework. The hardware elements used in the experimental scenarios were several USRP N210s. The implementation of the resource management software and the configuration of the SDR resources was realized with GNU Radio, a free and open-source software development toolkit that provides signal processing blocks to implement software radios [32]. In IRIS, the secondary network consists of four nodes organized in a full-mesh topology, i.e., every node has a direct connection to every other node in the network (Figure 5). The operation of the proposed autonomic cross-layer framework is first evaluated in the absence of PUs (Figure 5a), assessing in that way the achieved localized and distributed spectrum sharing among SUs. Subsequently, the focus is shifted to the demonstration of the transparent to the primary system operation of the secondary network. Hence, a PU is added to the topology (Figure 5b). Finally, the capability of the proposed mechanism to efficiently react to variations of the wireless environment is examined in respect to PU mobility (channel evacuation and idle time, PU reappearance, change of the occupied spectrum, etc.). Similarly, the secondary network in ORBIT consists of eight nodes organized in a full-mesh topology (Figure 5c), allowing us to verify the operational behavior of the mechanism in a larger, more realistic layout.