# MAC/PHY Comprehensive Visible Light Communication Networks Simulation
## 7 Conclusions  
In this work, a comprehensive MAC/PHY simulation environment for the IEEE 802.15.7 standard based on OMNET++ and an ad hoc MMCRT algorithm has been presented. Traditional network simulation software considers only the MAC operation and in some cases a simplistic physical channel approximation, which may lead to unrealistic outcomes. The main hypothesis that underlies this work is that considering the physical channel is capital for obtaining realistic network metrics. In order to prove this, three scenarios presenting three different network situations (no hidden nodes, a single hidden node, and no visibility between users) were essayed under saturated and not saturated traffic conditions. Furthermore, these network scenarios were simulated using two different physical scenarios, which showed unequal reflection coefficients on their ceilings. Several metrics (throughput, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Metric** & **Scenario 1** & **Scenario 2** & **Scenario 3** \\ \hline \multirow{3}{*}{Throughput} & 0.0533 (2 m) & & \\  & 0.009 (3 m) & 0.028 (2.5 m) \\  & 0.0394 (4 m) & & \\ \hline \multirow{3}{*}{QPDP} & 0.019 (3 m) & 0.1 (1 m) \\  & 0.024 (4 m) & 0.074 (1.5 m) \\ \hline \multirow{3}{*}{EPDP} & 0.054 (2 m) & 0.0 \({}^{\star}\) (2.5 m) \\  & 0.009 (3 m) & 0.003 (3 m) \\ \hline \multicolumn{3}{c}{Node Active Time} & & 0.088 (1.5 m) \\ \hline \multirow{3}{*}{Delivery Time} & 0.077 (0.5 m) & & \\  & 0.0 \({}^{\star}\) (2.5 m) & & \\ \cline{1-1}  & 0.0 \({}^{\star}\) (3 m) & 0.0 \({}^{\star}\) (2.5 m) & \\ \cline{1-1}  & 0.0 \({}^{\star}\) (4 m) & & \\ \cline{1-1}  & 0.0 \({}^{\star}\) (4.5 m) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Probability of failing after rejecting the null hypothesis for each one of the evaluated scenarios and metrics. Only the \(p\)-values smaller than a significance level of 0.1 are shown (the radii are between parentheses). * equals lower than 0.0001.  
node active time, delivery time, and packet delivery probabilities) were obtained after logging all the events of the 15 simulations that were executed for each case, and they were statistically compared using [PERSON]'s \(t\)-test. The developed network simulation environment comprised two main modules. The channel simulation module was based on the aforementioned MMCRT algorithm, and was used to obtain the channel impulse response of each link and therefore both channel gain (or path loss) and bandwidth. This information was used by the network modules (developed for OMNET++), which consisted of a PHY-layer submodule and a MAC-layer one. The PHY submodule detected collisions, simulated errors on the received frames and delivered messages to the MAC submodule. On the other hand, MAC operation was simulated following IEEE 802.15.7 recommendations, including random back-off mechanisms, superframe synchronization, and queuing. The obtained simulation results provided enough at-sight evidence about the differences between scenarios. Scenario 1 (no hidden nodes) was the closest to a MAC-only simulation since the nodes presented good CSMA/CA operation. However, as the network radii increased, the loss of coordinator-to-node link quality impaired performance on all the studied metrics. Scenario 2 showed similar metrics to Scenario 1 for small radii, but the metrics dramatically decreased above a threshold distance associated to a loss of visibility between nodes. On the other hand, Scenario 3 showed the worst behavior in general terms, suggesting that hidden nodes pose a likely harmful situation in VLC networks. From the traffic stress test carried out during the simulations, it can be concluded that a CAP-based network access could not be enough to allocate demanding applications in VLC. It was observed that although node active time was not affected by this parameter as expected, traffic accumulation led to massive packet losses, impairing QPDP and EPDP.