# Collision Avoidance Resource Allocation for LoRaWAN
## 5 Experimentation and Performance Results
### Performance Evaluation of the Proposed Solution  
In our first set of simulations, we compare a standard LoRaWAN network and a LoRaWAN network using our CARA scheme. We assume that 50,000 nodes are deployed and radio link conditions are ideal. As shown in Figure 10, our proposal outperforms the standard LoRaWAN achieving a maximum PER gain of 30.1% at a network load of 150 packets/s (PER was 71.4% in our proposal and 92.9% in standard LoRaWAN). Since this first set of simulations assumes ideal radio conditions, the packet errors are due to the collisions meaning that our solution significantly reduces the collision probability. This PER reduction allows the system to  
Figure 9: Collisions (**a**) with no border effect check and (**b**) avoiding the border effect. increase the maximum capacity (system throughput) from 21 packets/s to 41 packets/s, producing a relative gain of 95.2%. The second set of simulations considers a realistic urban scenario assuming the propagation model explained in Section 5.1. Two campaigns of simulations have been carried out with 1000 devices placed in the scenario. In the first campaign, the SF assignment have been carried out according to the ADR algorithm proposed in LoRaWAN standard [20]. Therefore, since we assumed fixed devices, the SF assigned to each device depends on the received sensitivity. In the second campaign, devices use the SFs in which they can transmit. For example, if a device can transmit in SF9, it will hop between SF9, SF10, SF11 and SF12. Additionally, the size of the scenario is also modified in order to understand the effect of the coverage area on the performance and SF usage distribution. We differentiate results for \"fast devices\" (those whose lower eligible SF is SF7, SF8 or SF9) and \"slow devices\" (those whole lower eligible SF is SF10, SF11 or SF12). Table 4 shows the simulated areas (from 2 km \(\times\) 2 km up to 10 km \(\times\) 10 km) and the distribution of \"fast devices\" and \"slow devices\" according to the propagation model and the gateway sensitivity (see Table 3). As expected, a smaller area has a higher percentage of \"fast devices\" since they are closer to the gateway and therefore the radio conditions are better. On the contrary, a larger area means that the percentage of \"slow devices\" increases due to the same reasoning. Figure 10(a),b represent the mean system throughput and PER for each campaign of simulations using coverage areas between 2 \(\times\) 2 km\({}^{2}\) to 10 \(\times\) 10 km\({}^{2}\). It can be seen that, for areas between 2 \(\times\) 2 km\({}^{2}\) and 8 \(\times\) 8 km\({}^{2}\), the CARA algorithm in this realistic scenario decrements the packet error ratio, achieving a maximum throughput up to almost 40% higher than the maximum achieved with ADR. However, with an area of 10 \(\times\) 10 km\({}^{2}\) we \begin{table}
\begin{tabular}{c c c} \hline \hline
**Area** & **Number of “Fast” Devices** & **Number of “Slow” Devices** \\ \hline
2 \(\times\) 2 km\({}^{2}\) & 658 & 342 \\
4 \(\times\) 4 km\({}^{2}\) & 646 & 354 \\
6 \(\times\) 6 km\({}^{2}\) & 632 & 368 \\
8 \(\times\) 8 km\({}^{2}\) & 623 & 377 \\
10 \(\times\) 10 km\({}^{2}\) & 562 & 438 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Number of devices transmitting in each group. Figure 10: Comparison of the throughput and PER for 50,000 devices between a standard LoRaWAN network and using CARA. (**a**) System throughput and (**b**) Packet Error Rate. can observed a reduction of the average throughput for medium/low network loads using CARA. As the coverage area grows, the number of \"slow devices\" also increases. This is common for both CARA and standard LoRaWAN. However, using CARA, \"fast devices\" also utilize slow SFs part of the time. This produces a concentration of network load being carried over slow SFs, causing a higher number of collisions. This effect is more noticeable with larger areas due to the spreading factors distribution. On the contrary, when the coverage area is smaller, there are more devices using cyclically all SFs.