# Robust Downlink Mechanism for Industrial Internet of Things Using LoRaWAN Networks
## 4 Results
### Effect of DROB Mechanism in Packet Delivery Ratio  
Another way to check the real effect of interference signals in the network, while observing the impact of the proposed DROB mechanism, is the packet delivery ratio (PDR) for the downlink traffic. This represents success in receiving the packets, and therefore with higher interference, a lower PDR is expected. It is worth noting the impact of the interference can differ due not only to the interference sources, but also the configuration of nodes and GW, which is where the DROB mechanism tries to optimize resources according to the environment variables. Given that the DROB mechanism is tuneable, and the number of samples (using the notation _C_x_ to identify the number of samples and the size of the window used) to perform the operations is configurable, the simulation was initially performed while varying this parameter in order to select the optimal value and check its impact, then selecting the candidate to test against the fixed DR configurations. Values of 20, 10 and 5 samples have been used. Values above 20 made the mechanism slow to react, as it waited to receive sufficient samples. On the contrary, lower values meant reacting more quickly, but also may have introduced too much variability and cause instability in the network as the configuration changed too often, hence the lower limit of five was set. In Table 3 it can be seen that this parameter does not significantly affect the results. In any case, C_20 was selected, as it showed overall better results and kept the sampling to 20, following the recommendations for the standard's ADR. This will be called simply the DROB. Once the DROB configuration was selected, Figure 11 below shows how the network responded in terms of PDR. These simulations kept the DR fixed to DR3 and DR5, which are the limits for downlink in a class B operation (due to restrictions in pingslot duration), and then activated DROB, which selected the DR used for each downlink packet sent dynamically during downlink. Figure 11: PDR for downlink results for each node in the network during the 24 h of the real scenario, and during one of the high frequency noise periods. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **C\_20** & **C\_10** & **C\_5** \\ \hline AVG & 85.86\% & 85.62\% & 85.60\% \\ MAX & 95.26\% & 94.74\% & 92.83\% \\ MIN & 72.35\% & 73.44\% & 71.21\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overall network results for DROB configurations with different sampling counters. These results were obtained after 24 h of simulation and show that the proposed DROB mechanism achieved results closer to the DR5 configuration, although it was able to keep more nodes above 75% PDR. If the analysis focuses on the periods of 1 h that introduce high frequency interference, then the results for the DROB mechanism showed improvement against the other configurations, as it adapted to channel conditions on the nodes that suffered from packet loss, keeping the DR as high as possible on the rest. By choosing the best DR configuration considering channel changes along time on a node per node basis, the result was that during the periods of time that noise was more frequent, DROB achieved better PDR results than the fastest (DR5) and the more robust (DR3) configurations. It was also able to send more packets that DR3 and better keep more nodes above 75% PDR than the other configurations. Table 4 shows the overall and the partial results for the whole network. Additionally, Figure 12 shows the average PDR per room (50 nodes), where it can be seen that further nodes suffered from more noise and interference and therefore benefited more from the DROB mechanism.