# Performance Evaluation of LoRa Considering Scenario Conditions
## 5 Results and Discussion
### Experimental Results
This is especially notable for the case of the suburban scenario (Figure 11c). Observing this behavior, we can conclude that many of the transmissions were received partially corrupted and then rectified in the receiver by the forward error correction (FEC) mechanism. Thus, in this case, the extra overhead is justified in exchange of the increased link robustness provided by the FEC procedure. Regarding the payload length (Figure 11b,d,f), observe that even considering two short payload lengths, namely 20 B and 40 B, a perceptible PDR improvement is attained when employing the shortest one. This can be an  
Figure 10: RSSI heat map in the rural scenario. (**a**) DR0; and (**b**) DR5. expected result, as shorter transmissions are less prone to be impacted by the effect of interferences, collisions, and other typical harmful effects inherent to wireless systems. In some tests, the attained values seem to be counterintuitive, e.g., in Figure 11b where the PDR for DR5 and payload 40 B is higher than the PDR obtained with a payload size of 20 B. These unusual values can be the result of the real traffic conditions experienced during the tests, like the speed at which the vehicle was circulating during transmission or the presence of sporadic obstacles between the base-station and the OBU. However, note that a clear trend is observed in the attained results. In the light of these outcomes, it could be stated that the best option is always employing a low DR, e.g., DR0, and high CR, e.g., 4/8, for ensuring long connectivity and link reliability. However, there is an important trade-off related to the time-on-air (ToA) of each transmitted packet motivated by the low bit-rates available in LoRaWAN, which cause that the channel occupancy of each transmission was not negligible. In order to illustrate this assertion, Table 4 shows the theoretical ToA for the different configurations considered in our experiments. As discussed in [21], the restricted duty cycle in the ISM bands together with the long LoRaWAN ToA severely limits both the number of nodes than can simultaneously connect to a single base-station and the number of transmissions per node  
Figure 11: Impact of the CR and payload length on the PDR for the three evaluated scenarios. (**a**) Urban scenario, impact of CR; (**b**) Urban scenario, impact of payload length; (**c**) Suburban scenario. Impact of CR; (**d**) Suburban scenario, impact of payload length; (**e**) Rural scenario, impact of CR; (**f**) Rural scenario, impact of payload length. per day. For that reason, it is highly desirable to keep the ToA as short as possible, hence we argue that, depending on the distance of the end-node from the base-station, different DR should be employed with the aim of balancing transmission reliability and channel occupancy. In order to exemplify this strategy, Figure 12 depicts the PDR attained for each DR, considering the end-node distance to the base-station in the urban environment. This study is done for the most favorable configuration, i.e., CR = 4/8 and payload of 20 B. Thus, observe that it is not necessary to employ the lowest DR in distances below 3 km, as a PDR of 100% is attained for the highest DR. This leads to a reduction of 96% of the ToA of each transmission, from 2499 ms down to 103 ms (please, see Table 5). Note that the greatest DR (DR5) would be only recommendable in the furthest links of above 5 km. With this strategy, the reliability of the system can be maintained by selecting low DRs in adverse transmission conditions. At the same time, the channel occupancy is controlled by making use of high DRs when the transmission conditions are favorable. Overall, both consequences permit to improve the system scalability [21]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**DR** & **Urban Scenario** & **Suburban Scenario** & **Rural Scenario** \\ \hline DR0 & 6.5 & 6.7 & 18.5 \\ DR1 & 5.4 & 5.8 & 13.7 \\ DR2 & 4.5 & 5.7 & 11.6 \\ DR3 & 4.4 & 5.3 & 11.5 \\ DR4 & 4 & 5.0 & 10.3 \\ DR5 & 2.8 & 5.5 & 9.6 \\ \hline \hline \end{tabular}
\end{table}