# Adaptive Multi-Channel Clustering in IEEE 802.11s Wireless Mesh Networks +
## 6 Experimental Validation
### Clustering in Static Topologies
#### 6.2.4 Results for Different Grid Sizes
[18]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Unit** & **Value P2** & **Value P1** \\ \hline CENT\_PERIOD & ms & 500 & 500 \\ \hline CENT\_THRESH & \# & **10** & 20 \\ \hline NC\_PERIOD & ms & **2000** & 5000 \\ \hline CH\_PERIOD & ms & **2000** & 5000 \\ \hline CH\_THRESH & \# & **0** & 2 \\ \hline PHASE\_DELAY & ms & **2000** & 10,000 \\ \hline PHASE\_PERIOD & ms & 500 & 500 \\ \hline PHASE\_TRIES & \# & **10** & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: CHaChA parameterization P2 (# indicates integer value without unit; changes to variant P1 are bold). Reprinted from ref. [18]. CHs is targeted. After CH announcement in phase 4, node 1 and 2 always joined the cluster of the MCH, which is preferred over other neighboring CHs. This strategy also favors the monitoring scenario, in which the synchronization of status information of nodes already managed by the MCH can be omitted. In phases 5 and 6, the CHs performed their virtual channel selection and claimed channel 36 and 40 from the predefined pool, as expected. By reaching phase 7, the initial cluster formation was complete. The currently allowed emergence of CHs in neighborhood to the MCH causes clusters to be formed even in small topologies that do not require further subdivision (see \(2\times 2\) and \(3\times 3\) grids). However, as part of the evaluation, this behavior was intended to allow CHaChA to be studied in the laboratory setup. For practical use, CHs in close proximity to the MCH could be prevented or a minimum ALM distance could be mandated, depending on the overall node count or estimated network diameter. Similarly, a minimum network size could be defined above which cluster formation is performed at all. **3 \(\times\) 3-node grid:** In the topology with nine nodes, four different cluster constellations emerged (see Figure 15), with the central node 7 always reliably obtaining the MCH role. In the \(3\times 3\) grid, generally only nodes 2, 6, 8, and 12 were considered as additional CH candidates, as they had the highest number of neighboring nodes after node 7 (NC = 5). In the most frequent constellation (Figure 15a, 7/10 measurements), nodes 6 and 8 each won the contest with nodes 2 and 12 due to dominant CENT metrics. In contrast, the remaining three constellations (Figure 15b-d, 1/10 measurements each) comprised only two clusters and differed in the position of the second CH. Due to variations in the ALM cost between nodes, from which the CENT value is derived as a weighting factor of the WNPR metric, in each of these measurements, a different pair of diagonally adjacent PCHs with dominant WNPR competed with each other, resulting in only a single CH being selected besides the MCH. As in the \(2\times 2\) setup, the remaining nodes preferentially joined the MCH cluster in all constellations. Balancing after reaching phase 7 would lead to a roaming of edge nodes into the still unoccupied clusters. Figure 15: Cluster constellations in the \(3\times 3\)-node grid for parameterization P2 (cluster channels (“C#”) highlighted in color; occurrence rate given in %). Reprinted from ref. [18]. 4 \(\times\) 4-node grid: As in the \(2\times 2\) grid, no symmetric central node position existed in the \(4\times 4\) topology. Accordingly, the nodes of the inner square (nodes 7, 8, 12, and 13) were the expected candidates for the MCH role and another CH due to their dominant CENT metric and maximal neighbor count (\(\text{NC}=8\)). In the total of ten measurements, ALM variations led to nine different constellations (see Figure 16), which differed in the selected CH pair and / or the subsequent joining decisions of the CMs. While nodes adjacent to the MCH preferentially joined its cluster, nodes further away again made their decision based on the ALM costs to the CHs. As a result, balanced cluster sizes already emerged in constellations 4, 7, and 9 (Figure 16d,g,i). Even in constellation 6 (Figure 16f), the difference was only one node. Subsequent CM roaming would lead to a balancing of cluster sizes here as well.