# Autonomic Network Management and Cross-Layer Optimization in Software Defined Radio Environments
## 5 Experimental Results
More specifically, this scenario involves the presence of multiple SUs in a constrained space, potentially coexisting with PUs. Such a case may correspond to a peer-to-peer network where SUs exchange files, or a sensor network where devices exchange localized information by opportunistically accessing the licensed spectrum. Regarding Gibbs sampling, all sites update their state sequentially within a sweep, one at each epoch according to the selected visiting scheme (the ascending numerical order of IDs). An annealing schedule of the form \(T(w)=\frac{c_{0}}{ln(1+w)}\) is adopted, where \(T(w)\) is the temperature of the \(w^{th}\) sweep and \(c_{0}\) is set to \(2.0\). The secondary network is assumed characterized by best-effort traffic, therefore the parameters of the sigmoid function are chosen as \(A=2\), \(B=-1\), \(C=2\) and \(d=0\). Likewise, the parameters of the potential functions are set to \(\{\lambda_{1},\lambda_{2},\lambda_{3}\}=\{4,2,2\}\) for IRIS and \(\{\lambda_{1},\lambda_{2},\lambda_{3}\}=\{2,3,5\}\) for ORBIT. In both cases, the spectrum nominally assigned to PUs and opportunistically accessed by SUs is in the area of 3550-3800 MHz. The channel bandwidth (both control and data) is equal to 10 MHz and the control channel has a central frequency of 3400 MHz. Furthermore, we assume that the interference radius is equal to the transmission radius, hence the neighborhood of each SU extends within a maximum distance of \(R_{t}+R_{i}=2\cdot R_{t}\). Finally, \(\delta_{1}\) and \(\delta_{2}\) are both equal to 500. The experimental scenarios executed are summarized in Table 1.  
Each experimental scenario is independent and has its own configuration file that defines the transmission rounds to be conducted and other operational parameters, like the total number of channels along with their respective central frequencies. The framework assumes time-slotted operation, with every time-slot further split into smaller frames for the execution of different (cognitive) functions. Every transmission round can be viewed as a separate iteration of the resource management \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \# & **Testbed** & **PU** & **No. of SUs** & **No. of Channels** & **Sweeps** & **Transmissions** & **Collisions a ** \\ \hline
1 & IRIS & No & 4 & 5 & 50 & 47 & 3 \\
2 & IRIS & No & 4 & 5 & 50 & 47 & 4 \\
3 & IRIS & No & 4 & 3 & 30 & 47 & 5 \\
4 & IRIS & No & 4 & 5 & 50 & 36 & 1 \\
5 & IRIS & Yes & 4 & 4 & 40 & 47 & 3 \\
6 & IRIS & Yes & 4 & 5 & 50 & 47 & 0 \\
7 & ORBIT & No & 8 & 6 & 60 & 57 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental Scenarios. Figure 5: Network Topology: (**a**) 4 secondary users (SUs) full-mesh without primary users (PUs). (**b**) 4 SUs full-mesh with one PU. (**c**) 8 SUs full-mesh without PU. Node IDs correspond to the actual ones employed during the execution of the experiments. routine. The latter describes the complete operation of a SU during one time-slot. In all scenarios there are three kinds of data transmissions: 1-hop, 2-hop and 3-hop transmissions. The implementation of the proposed RCA mechanism presents enhanced reconfiguration capability as it adapts efficiently to different scenarios, accomplishing a key performance objective of the proposed approach. More specifically, the algorithm presents fast convergence, as it is indicated by the number of sweeps, taking into consideration the number of MNs and the number of channels used in the experimental scenarios, as depicted in Table 1. The latter was indicated by the simulation results provided in [31] and now it has been experimentally verified. Additionally, it has been shown that a relatively small number of collisions occurred, considering all experimental scenarios, confirming the efficiency of the proposed approach. As it was expected, in resource constrained scenarios (according to the number of channels used and the number of MNs) we noticed a small increase in the number of collisions, but again at an acceptable degree.