# LaRaCog: A Protocol for Cognitive Radio-Based LoRa Network
## 7 Results  
The evaluation is based on comparison of the rejected packet rate between LoRaWAN and LoRaCog using different scenarios that will be explained in this section. As a reminder and for demonstration purposes, the simulation is using 868 MHz frequency for LoRaWAN (such as in EU) and an additional cognitive frequency 438 MHz for LoRaCog along with 868 MHz. LoRaCog can be configured to utilize multiple licensed or unlicensed frequencies, which will generate better performance. Figure 9 illustrates the comparison between LoRaWAN 868 MHz and different splits of LoRaCog EDs between 868/438 MHz bands. For both protocols, 4 GWs were used to detect the packets from 500 EDs. If a packet is received by any of the 4 GWs, it will be successfully decoded and not rejected. The result is better for LoRaCog, and rejected packets decrease when the EDs are more distributed among the cognitive frequencies. In this example, LoRaWAN with 500 EDs, the rejected packets percentage was above 50% while using LoRaCog, it goes down to 24% (using 10 by 90 split). To illustrate the effect of the proposed LoRaCog on the number of needed GWs, Figure 10 compares LoRaWAN when using 4 and 6 GWs with LoRaCog using 4 GWs. The figure shows that LoRaWAN with 6 GWs has the same performance as LoRaCog 4 GWs when 60% of EDs are on 868 MHz and the rest are on 438 MHz. However, LoRaCog has lower rejected packets from LoRaWAN 6 GWs when the percentage of the EDs operating on the cognitive channel (438 MHz) increases. Therefore, LoRaCog can reduce the investment of infrastructure, and at the same time, it assures spectral efficiency that is utilized fairly between EDs, avoiding congestion where possible. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Details** \\ \hline Number of GWs & 4 \\ Number of EDs & 500 \\ Distribution of ED and GWs & Uniformly distributed \\ Frequency & LoRa 868 MHz/LoRaCog 868 \& 438 MHz \\ Power & 25 mW \\ Bandwidth & 125 KHz \\ Area & Small–medium city \\ Simulation & Monte Carlo \\ Model & Okumura-Hata \\ Spreading Factors & Same as LoRaWAN \\ Sensitivity & Same LoRaWAN \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Matlab Simulations Parameters. Figure 8: Representation of the EDs and the GWs distribution in our simulations. The forthcoming simulation considers the probability of the re-appearance of PUs. PU may return to be active on the cognitive channel, leading to a collision with ED transmission. However, LoRaCog may strongly reduce the effect of this re-appearance for two main reasons. Primarily, the NS will be doing analysis for the spectrum sensed by GWs on a continuous basis and will recommend only those with very low activities from PUs. Secondly, LoRaCog protocol is acting similarly to LoRaWAN and its characteristics; thus, the performance of LoRaCog is limited to the number of sensors. Figure 10: LoRaWAN 4 and 6 GWs vs. LoRaCog 4 GWs. Figure 9: The evolution of the rejected packets for both LoRaWAN 868 MHz and LoRaCog 868/438 MHz for different percentage splits. ED will be sending short messages in milliseconds and not frequently (once per day for battery operated EDs), so it will not interfere with PUs. Figure 11 shows the performance of LoRaCog compared to LoRaWAN assuming PUs will come back to the network with a probability of 1%. PUs interrupt the transmission of EDs using cognitive frequency. The active number of PUs are simulated as an equal number of rejected packets from those EDs on the cognitive side. LoRaCog shows better performance even with active PUs in the network and in parallel reduces congestion. Figure 12 illustrates the behavior of LoRaCog compared to LoRaWAN for 5% probability of PUs re-appearance on the operating cognitive frequencies. LoRaCog still performs better than LoraWAN for the different split combinations for both scenarios: when the majority of EDs operate on the cognitive channels (Figure 12a) or when operating on the classical channels (Figure 12b).