# LTM-LoRaWAN: A Multi-Hop Communication System for LoRaWAN
## 4 Performance Evaluation
### System Model and Configuration Parameters  
The simulation model in this study is based on the Framework for LoRa (FloRa) simulation model [25], which can be found at [26]. FloRa itself is developed based on the OMNeT++ network simulator and uses the INET framework. The simulation model has been modified to support the proposed system. It supports all the functionalities of the proposed system, which has been introduced in the previous section, including the identification of being out-of-range of a gateway, the procedure of medium access, and the forwarding mechanism.  
The log-distance propagation model is the used model for path loss and propagation. It provides an estimation for an urban environment. It calculates path loss according to the following equation.  
\[PL=PL_{d_{0}}+10n\text{log}\left(\frac{d}{d_{0}}\right)+x_{g} \tag{1}\]  
The \(PL_{d_{0}}\) is a path loss value for path loss calculation at 0 distance. The \(n\) parameter shows the effect of the range on the data rate. The \(x_{g}\) is a Gaussian random variable with zero-mean and \(g\) presents standard deviation. The used path loss model uses 1000 m for \(d_{0}\), 128.95 dB for \(PL_{d_{0}}\), 2.32 for \(n\), and 0 dB \(g\). The values were derived from real experiments in [27].  
End devices are deployed in a 20 km \(\times\) 20 km square area. For each simulated experiment, about 20% of the participating LoRa end devices were distributed close to the border of the area to allow the evaluation of the proposed system. The number of end devices varied from 100 to 1000 devices in the step of 100 end devices. One gateway was used and located in the middle of the simulation area. The characteristic of the SX1272 Lora device is used to give the simulator more realistic parameters, as it is an industry standard developed by Semtech [28]. The ADR mechanism is enabled for all the end devices and the network server as well. Hence, SF and transmission power are adopted using the ADR mechanism whenever it is needed based on the position and the circumstance for each single device. Each end device wakes up periodically to generate traffic with 30-byte sizes based on the used send interval. Two intervals were used, sixty minutes and ninety minutes. Every single experiment was repeated 10 times with a duration of 10 days. The performance of the proposed system was compared to the baseline, a LoRaWAN network operating one-hop communication in similar simulation configurations and parameters. Table 1 highlights the parameters used in the carried-out simulations.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Simulator & OMNeT++ \\ Framework & FloRa and INET \\ Simulation Area & 20 km \(\times\) 20 km \\ Gateways & 1 \\ Sensor Nodes & 100–1000 \\ ADR & Enabled for sensors and Network server \\ Spreading Factor & 7–12 \\ Transmission Interval & 3600–5400 s \\ Packet Size & 30 bytes \\ Duration of Simulation & 10 days \\ Repetition & 10 times for each single scenario \\ Path Loss Model & Log distance \\ Bandwidth & 125 kHz \\ Coding Rate & 4/8 \\ Carrier Frequency & 868 MHz \\ \hline \hline \end{tabular}
\end{table}
Table 1: Simulation Parameters.