# Analysis of Bidirectional ADR-Enabled Class B LoRaWAN Networks in Industrial Scenarios
## 6 Results
This is due to the fact that devices nearer to the gateway suffered more interference as there were more packets from other devices using the  
Figure 10: Results of SF for downlink traffic configured in every node at the end of the simulation, overlaid on the site map. Figure 9: Results of SF for uplink traffic configured in every node at the end of the simulation, overlaid on the site map. channel. With a fixed SF, all nodes may interfere with one another, while enabling the ADR means nodes in different regions do not interfere, as the gateway can recover packets independently from all the SFs. This translated into a difference of 1.5 to 1.8% in PDR between fixed SF7 and ADR (depending on upload periodicity). For fixed SF12, the results were worse in all configurations, as it combined all EDs interfering in the same SF with the longer time-on-air values, making collisions more probable. In Figure 11, the PDR for every ED in the scenario can be seen, and it is clear that devices in the first warehouse, as well as the ones near the walls in the rest of the scenario, show the worst PDR values. This is due to the combination of walls, as well as the distance between nodes on the vertical axis being one-half the distance between nodes on the horizontal axis. From the point of view of downlink traffic, using the ADR mechanism described did not impact the PDR, as EDs achieved more than 99% of successful receptions, but this was mainly due to the use of class B operation mode, where devices have an assigned and scheduled time slot, so the success probability was already maximized; thus, this mechanism may only be interesting from the energy consumption point of view in this scenario. Nevertheless, even noisier or variable scenarios may take advantage of adapting the SF up and down to palliate losses and optimize PDR. While these results may tempt one to disregard using ADR, it must be taken into account that the difference between using it and not using it increases with the distance between ED and the gateway; thus, for different scenarios with different conditions, the choice should be supported by further simulations, given that the ADR mechanism has been validated to work as expected. These results have a serious impact on the energy consumption of devices. Equation (10), where I_tx is the current consumption during transmission and V is the voltage fixed at 5 V, is used to calculate the energy used for transmission in 24 h according to the SF achieved due to the ADR. Figures 12 and 13 show that by choosing lower SNR\({}_{\text{sc}}\), lower SFs are reached faster, and therefore, EDs spend less time transmitting, which translates to lower energy consumption. Configuring the ADR mechanism to only use 5 samples as SNR\({}_{\text{sc}}\) reduces the network energy consumption by one-half compared with the commonly used value of 20 samples. \[\text{E}_{\text{\_tx\_consum}}=\sum_{\text{SFI}=7}^{\text{SFI}=12}\text{I}_{ \text{\_tx\_}}*\text{V}*\text{T}_{\text{airtime\_SFi}}*\text{T}_{\text{\_in \_SFi}}/\text{T}_{\text{\_tx}} \tag{10}\]  
Figure 11: Uplink packet delivery ratio (PDR) achieved for every ED for different configurations with fixed SF versus ADR activated. Regarding the downlink stage, when nodes receive packets, the power overhead of class B operation is a function of the following:  
* The time-on-air of the beacon, which is region-specific (SF9/125 kHz) => beacon time-on-air \(\sim\)160 ms;
* The periodicity of the ping slots (two ping slots per beacon period in this case);
* The ping slot SF;
* The class B downlink periodicity. Taking this into account, the main energy drainer for an ED is the reception of beacons and the minimum time it must be listening during its assigned ping slots even if there are no incoming packets.