# Channel Access in Wireless Smart Grid Networks Operating under ETSI Frame-Based Equipment Rules
## 5 Performance Analysis
### Homogeneous Networks  
To evaluate overall performance in the homogeneous case, we measure the metrics defined previously as a function of an increasing number of nodes. We use two simulation approaches to depict crucial differences in the behavior of the variants. The first is the 'optimized parameter' approach. We select per-node parameters such that the performance of the whole network is similar, regardless of the number of contending nodes. To achieve this goal, we carefully tune the variant parameters (with a parameter sweep) to achieve the best performance for each case. These parameters include node shift (for perfect node coordination), FFP and COT durations, as well as variant-specific parameters. Examples of these parameters for standard FBE and fixed-muting FBE are given in Table 2. A complete listing, containing all variants, is provided in the online Supplementary Material ([[https://github.com/marcink2138/NRUsharp/blob/main/tests/README.MD](https://github.com/marcink2138/NRUsharp/blob/main/tests/README.MD)]([https://github.com/marcink2138/NRUsharp/blob/main/tests/README.MD](https://github.com/marcink2138/NRUsharp/blob/main/tests/README.MD)), accessed on 24 December 2023). In the second, 'non-optimized parameter' approach, we use fixed parameter values for a varying number of contending nodes. The values are arbitrarily selected as those that optimize performance for eight competing nodes. For the case of optimized parameters, the results are presented in Figure 12. We expect to see high fairness (indicative of good resource sharing) as well as low channel access delay and high channel efficiency (both indicative of a low number of collisions and'silent' periods). We observe that all variants are able to achieve a constant and high value of fairness, close to one. The delay values increase with the number of competing nodes (which is expected) and are larger for the three random-backoff-based variants. There is more variance in the channel efficiency results. Although most variants can reach high values, four of them perform significantly worse. In the case of DB FBE, this is caused by the expensiveness of its backoff algorithm, whose convergence time grows with the number of nodes. For floating FBE it is impossible to achieve perfect node coordination due to its random offset before COT, while enhanced FBE suffers from collisions. Interestingly, the channel efficiency of random-muting FBE increases due to the existence of obligatory muted periods and their randomness. The best performance efficiency is achieved by standard FBE, as well as fixed-muting BITR and greedy-enhanced FBE. In particular, with a properly selected node shift, FFP, and COT length, it is possible to achieve a constant and almost perfect value of channel efficiency for standard and fixed-muting FBE. BITR FBE and greedy-enhanced FBE successfully reduce the number of possible collisions by either shortening the idle time after an unsuccessful backoff or constant channel sampling, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Nodes**} & \multicolumn{2}{c}{**Standard FBE**} & \multicolumn{3}{c}{**Fixed-Muting FBE**} \\ \cline{2-6}  & **FFP (\(\mu\)s)** & **COT (\(\mu\)s)** & **FFP (\(\mu\)s)** & **COT (\(\mu\)s)** & \(N\) \\ \hline
2 & 1000 & 491 & 1000 & 491 & 0 \\ \hline
4 & 2000 & 491 & 1000 & 491 & 1 \\ \hline
8 & 4000 & 491 & 1000 & 491 & 3 \\ \hline
16 & 8000 & 491 & 1000 & 491 & 7 \\ \hline
32 & 10,000 & 303 & 1000 & 491 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Optimized simulation parameters for standard FBE and fixed-muting FBE for homogeneous networks. respectively. These features result in better channel utilization than in the case of the similar enhanced FBE using the same node shifts and maximal backoff counter values. In Figure 13, we provide the simulation results for the non-optimized case. As expected, the measured metrics achieve the best values for eight nodes.