# Smart City Pilot Projects Using LoRa and IEEE802.15.4 Technologies
## 5 A Smart City Testbed: The Rigers Project
### Network-Level Performance Assessment via Simulations
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Transmit Power, \(P_{l}\) & 14 dBm \\ Antenna gains, \(G_{\mathrm{t}}=G_{\mathrm{r}}\) & 2 dB \\ Penetration Loss, \(PL_{\mathrm{add}}\) & 12.5 dB \\ Shadowing standard deviation, \(\sigma\) & 9 \\ Protection ratio, \(\gamma\) & 0.3 dB \\ Payload size & 10 Bytes \\ Bandwidth & 125 kHz \\ Frequency of packets generation & 1 h \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation Parameters. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Spreading Factor** & **Bit Rate (Bit/s)** & **Indicative Receiver Sensitivity [dBm]** \\ \hline
12 & 250 & \(-\)137 \\
11 & 440 & \(-\)135 \\
10 & 980 & \(-\)133 \\
9 & 1760 & \(-\)130 \\
8 & 3125 & \(-\)127 \\
7 & 5470 & \(-\)124 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Bit Rates and Receiver Sensitivities for the 125 kHz bandwidth. on the roof of a building and the multi-sensor boards will be deployed indoor, this factor accounts for the additional loss, due to the penetration of the wall. Finally, \(s\) is a Gaussian random variable having zero mean and standard deviation \(\sigma\), representing shadowing. We consider two cases: (i) gateway equipped with a single receiver, which can be tuned to a specific channel (125 kHz bandwidth) and synchronized on a specific spreading factor value; (ii) gateway equipped with different receivers, such that it is able to decode signals transmitted using different spreading factors (again a single channel of 125 kHz bandwidth is considered). The first case refers to the receiver that will be used in the RIGERS project, while the second case refers to a LoRaWAN gateway. In the second case, as stated in Section 3.2, all nodes start using \(SF=7\) and then, every two retransmissions, \(SF\) is increased by one to mitigate coverage issues (curves related to this case are denoted as \"variable \(SF\)\" in Figure 8). After three hours of simulation, \(SF\) is reset to 7. Figure 8a,b report the percentage of packets correctly received by the gateway (packet success rate--PSR), as a function of the number of buildings deployed, \(N\), for the Navile and Saragozza districts, respectively. Both the cases of variable and fixed \(SF\), when considering different values of \(SF\), are reported in the figures. In the case of Navile, when setting low values of \(SF\), the network is limited by connectivity and the PSR slightly depends on \(N\). Indeed, the ideal (when shadowing is not present) transmission range is within 0.3 km (obtained when setting \(SF=7\)) and 0.8 km (for the case \(SF=12\)), while the maximum distance covered in the scenario is 0.85 km. This connectivity problem is mitigated when setting \(SF=12\), allowing to reach more buildings (lower receiver sensitivity); however, as \(SF\) increases, the airtime increases as well (1.18 s when \(SF=12\), versus 0.05 s when \(SF=7\)), resulting in a larger collision probability and a reduction of the PSR when \(N\) increases. Since nodes use a simple ALOHA protocol to access the channel, an increase in airtime brings to a performance worsening in interference limited scenarios. In conclusion, \(SF=10\) is the best case, allowing a good trade-off between connectivity and collision issues, and allowing to achieve a PSR larger then 90% for up to 400 nodes/buildings. In this scenario, the strategy suggested by the standard to dynamically set \(SF\) (variable \(SF\)) does not allow to obtain the best performance. This is due to the fact that the scenario is limited by connectivity, therefore many nodes do not receive the ACK, increase \(SF\) and after some transmissions many nodes tend to use \(SF=12\), which is not the best value because of collisions (see the curve \(SF=12\)).