## 3 Literature Review Results
### Literature Review Conclusions  
Based on the presented information, the predominant technology to geographically locate transit vehicles continues to be GNSS because it allows continuous tracking. Some other technologies such  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Article** & \begin{tabular}{c} **Communication** \\ **Technology** \\ \end{tabular} & **Service** & \begin{tabular}{c} **Based on** \\ **ITS** \\ \end{tabular} & \begin{tabular}{c} **Implementation** \\ **Type** \\ \end{tabular} & \
\begin{tabular}{c} **Applied** \\ **Environment** \\ \end{tabular} &
\begin{tabular}{c} **Use of** \\ **Security** \\ \end{tabular} \\ \hline i-Car System: & & & & & & \\ A LoRa-based Low-Power & & & & & & \\ Wide-Area Networks & LoRa & General & No & Simulation & Not specified & No \\ Vehicle Diagnostic System & & & & & & \\ for Driving Safety [64]. & & & & & & \\ \hline Traffic Light Mobility & & & & & & \\ Management Prototype & & & & & & \\ for Amballores, & LoRa & Amballores system & No & Real & & \\ Under the Smart City & & & & & & \\ Concept [65]. & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._as ZigBee, WiFi, RFID, and Bluetooth can be used to locate vehicles, but only when it passes very close (a few meters) to a certain point where the reader device is located, for example at stops to pick up/drop off passengers.  
Regarding the communication technology between the vehicles and the Transit Management Center, cellular communication technologies still prevail; however, some important emerging technologies were identified. LPWAN technologies have been evaluated in some documents, identifying LoRa as a promising technology (comparing it with technologies such as Sigfox or NBIoT), for its already mentioned features.  
A gradual increase in the use of applications with security was also observed in the proposals for various fields of systems (communications, authentication, and information security), Although, in most cases, appropriate tests are not conducted to validate the proposals, this increase infers the need to implement security mechanisms in mobility services systems.  
The security applications in the analyzed documents focus on various aspects. Authentication of vehicles is one of them; various strategies are proposed to reduce time and improve the efficiency of this function. Other proposals focus on communication security, proposing improvement algorithms on the security protocols such as LTE, emphasizing the need to improve security requirements such as confidentiality, integrity, privacy, availability, and nonrepudiation. Compliance with these requirements is important for the exchange of data between the vehicles since, otherwise, the information could be vulnerable to external attacks and inappropriate handling. It is also important to highlight security in access to the system, guaranteeing that unauthorized parties are not allowed to access the system. The issue of anonymity must also be considered in the security component. Travelers, for example, do not need to identify into the system to obtain certain information; while other actors, such as vehicles and operators, need to identify themselves in order to monitor their actions.