# A Low Energy IoT Application Using Beacon for Indoor Localization
## 3 Background on Methods and Technologies for Indoor Localization  
The study of indoor localization arises from the need to locate certain objects or people in large buildings, offices, museums, hospitals, etc. The term localization system refers to a system capable of calculating and determining the spatial position of a specific object or a specific person. In reality, the position data are not the only parameters that can be obtained: objects can also be monitored through temperature, movement and light sensors.  
In addition to locating objects and people in real time, it is therefore possible to do the following:  
* Trace the path of objects/people at a certain time;
* Calculate the parking times of an object/person in a certain area;
* Analyze the various interactions between objects and people.  
In a localization system, it is possible to distinguish, in the same area, both fixed points, known a priori, and mobile points, identified through relations on the coordinates of the first ones. An indoor localization system has the ultimate purpose of returning, as accurately and quickly as possible, the user's position with respect to a spatial reference system. Specifically, for indoor environments, the position is determined and represented using the coordinates of a Cartesian system, as we are not interested in determining the position according to the characteristics of the earth.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Technology** & **Accuracy** & **Power Consumption** & **Cost** \\ \hline Wi-Fi & \(\sim\)1–5 m & High & Low \\ Bluetooth & from 30 cm up to a few meters & Low & Low \\ RFID & \(\sim\)1–5 m & Low & Passive: Low \\ UWB & \(\sim\)1–5 m & Low & High \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overview on indoor localization systems.  
The other reference system that is adopted, this time for outdoor environments, is the one called \"ellipsoidal reference system\" since it is more suitable for large and complex geographical locations. Localization techniques are divided into four general methodologies [26; 27; 28]:  
* Angle of Arrival (AOA);
* Time of Arrival (TOA);
* Time Difference of Arrival (TDOA);
* RSSI-based method.  
The last methodology was analyzed and addressed during the internship experience: the idea behind this technique is to exploit, as we will see in the next paragraph, the power signal of the devices in order to obtain useful information from translation into distance. In the following paragraphs, however, the other methodologies will also be described and analyzed in order to fully understand both their basic functioning and how localization in an indoor environment can take place.  
Table 2 shows the advantages and disadvantages of the various methodologies presented up to now.  
As can be seen from this table, the use of the RSS-based method is much simpler, more intuitive, less expensive than the other algorithms and, moreover, it is not necessary to synchronize the various devices with each other. Comparing instead the technologies of Table 1, it is understood how it is preferable--for power consumption, costs and accuracy--to exploit Bluetooth technology.