# Analysis of Low Cost Communication Technologies for V2I Applications
## 5 Discussion  
After monitoring the performance of the modules for V2I communication, the most important conclusions, which will let us go on with the study, are highlighted. Based on results, a decision tree was made, as can be seen in Figure 9. The aim was to show strengths and weaknesses of each technology by means of a possible application. Regarding the decision tree, depending on the case, it recommended one technology or another. An example of the different five cases:  
1. Small area + less time + more vehicles: For instance, urban areas. Areas with high traffic flow and which could require a quick reaction in case that (for instance) accidents takes place. 2. Small area + less time + less vehicles: For urban areas with less importance or where the flow of traffic is less than case 1. In this way, there was more time to take an action. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Comparison of Results**} \\ \hline
**Features** & **nRF24L01+** & **XBeev (ZigBee)** & **WiFi b/g/n/ac (embedded)** \\ \hline
**Range** & \(<\)600–1000 m (depends on height) & \(<\)500–1000 m (depends on height) & \(<\)100 m \\
**Latency** & 40–350 ms & 1000–3500 ms & 14–100 ms \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Module performance. Figure 9: Device decision tree. Small area + high time: Peri-urban areas. Outskirts of the city, where it was possible to give information to the drivers, improving their route before going into the city. 4. Large area + high time: Highways or national roads. In this case, the technology ZigBee would send informative messages in broadcast mode (accidents, road works, and traffic signals), so there was no need of interaction. 5. Large area + less time: For example, intersections in national roads or highways, roads with low traffic flow, where it was possible to require a quicker reaction or response. Contrasting technologies, the best technology in terms of communication speed is Wi-Fi. However, its really short range is an inconvenient because this device is out of our criteria of short/middle range. For this reason, this technology was not further tested. Meanwhile, the technology based on ZigBee was the slowest one, although it had a wide range which paid off for the lack of speed. For example, with a vehicle speed at 50 km/h, driving 1000 m, it spent 72 s, which was enough time for a good communication. The best ratio range/latency was offered by the nRF24L01+ module. It covered up to 1000 m, sending messages every 350 ms, allowing us to set a network with more flexibility than the one set by ZigBee because it sent messages more frequently. The behavior also depended on the type of bus used for the physical connections (Table 2). Arranging in decreasing speed order: The technology embedded was faster than SPI connection, which was faster than UART or USB. ZigBee made use of UART and USB connections, and nRF24L01+ made use of SPI connections. Based on the information above and the available information of the communication technologies in Section 3.2, we concluded that ZigBee is designed for home automation or applications, where it can operate with a low power consumption. That is the reason why it sends messages slowly. ZigBee is ready for slower data delivery. Although it is a limitation, this technology will go on under study. On the other hand, with the aim of knowing the influence of the microprocessors in the operation of the technology, we contrasted our results with the nRF24L01+ study carried out in [11]. They had latencies of 128 ms, although it was a variable measure. Its maximum latency measured was 300 ms, against our maximum latency of 350 ms. This gap between studies was due to the microprocessors (because the device configuration was the same). Meanwhile, in [11] they employed two Arduinos UNO. In this study an Arduino and a Raspberry were used. So the combination employed in [11] was faster and stronger. Using the same microprocessor made easy the synchronization because the devices had the same clock speed.