## 6 Alternative Tracking System  
A common use of many systems integrated with beacons is for indoor location and user tracking [31]. Although those systems do not offer an exact location, they are widely used to indicate whether a user has been close to the area where the beacon is or not. By having direct connectivity to the Internet, these systems are able to record the time and approximate location of each user in real time. In this section, an alternative system is described to provide a solution for the case of areas without coverage, which takes advantage of the FatBeacon protocol implemented in systems where the emitted information can be altered (such as Raspberries). Using FatBeacon devices, the system can be used to indirectly send data to users, through a secure and anonymous communication protocol. In this way, the information shared by the users can be used to provide anonymous statistical data that allow creating users' tracking maps, among other possibilities. The main advantage, apart from the generation of statistical data, is that passive monitoring of the different users in the area without coverage is possible. To illustrate the idea, we use a basic example (see Figure 14) of a path that is very popular with tourists. The image shows the same scenario in three different stages (\(t_{0}\), \(t_{1}\) and \(t_{2}\)) with  
Figure 13: Screenshots of the developed application. POIs or beacons (\(p_{0}\), \(p_{1}\),..., \(p_{n}\)). The section between \(p_{1}\) and \(p_{n-1}\) has no Internet coverage, so an Internet connection only exists in the \(p_{0}\) and \(p_{n}\) nodes. In the image, two different users \(u_{1}\) and \(u_{2}\) are distinguished. Before starting the trail, the user \(u_{1}\) generates a random identifier for the application. The right side of the image shows how the information is stored and exchanged by both users. In the image we see that:  
* At \(t_{0}\), the user \(u_{1}\) starts the tour and moves through the area without coverage throughout time. During the trip, the application that \(u_{1}\) has on his/her mobile phone sends information and has a conversation with FatBeacons sharing the current tracking. At the same time, each FatBeacon stores user information anonymously (including the ID) generated by \(u_{1}\) and the time that has passed. The beacon also stores the points previously visited by \(u_{1}\). * At \(t_{1}\), the user \(u_{1}\) comes across the user \(u_{2}\), which has been near \(p_{1}\) for a few hours. During these hours, the user \(u_{2}\) sends to the same beacon the updated tracking information (adding the new registration hours). While \(u_{2}\) continues doing various activities at that spot, \(u_{1}\) continues on his/her way, but before that, the information that both have generated and that is stored in the beacon \(p_{1}\) is shared by both. Now, \(u_{1}\) has his/her own information and the information updated by \(u_{2}\) until that time. Likewise, \(u_{2}\) will have his/her own information and data generated from \(u_{1}\). This exchange of information is automatic, such that it is not necessary to have previous contact or permission from the other user. * At \(t_{2}\), the user \(u_{1}\) reaches the end of the trail where she/he has an Internet connection. Automatically, the \(u_{1}\) tracking data from the beginning of the trail to the end are sent to an information server. Similarly, \(u_{2}\) data from the beginning until he/she came across \(u_{1}\) is also sent. In an extended example, we consider a map of the real path (see Figure 15) shown in Figure 11. A starting point for user [PERSON] (\(u_{1}\)) and a different starting point for [PERSON] (\(u_{2}\)) have been set over the map. The areas marked with the red squares are areas where there is no Internet connection or network coverage. Besides, there are four FatBeacons along the trail. [PERSON] follows the route through \(P_{1}\), \(P_{2}\) and \(P_{3}\) beacons, while [PERSON] follows the route \(P_{0}\), \(P_{2}\) and \(P_{3}\).