# A Low Energy IoT Application Using Beacon for Indoor Localization
## 3 Background on Methods and Technologies for Indoor Localization
#### The Development of Bluetooth Technology  
Bluetooth is a short-range wireless transmission standard, developed by the Blue-tooth Special Interest Group--SIG, operating at frequencies between 2.4 GHz and 2.485 GHz, which allows multiple devices to communicate and exchange data and information. of any kind. The first versions marketed guaranteed data exchanges between devices at a maximum speed of about 723.1 Kbit/s, while with subsequent releases (Bluetooth 2.0 and Bluetooth 4.0), the amount of data exchanged in a single second was increased. This technology is very useful and used thanks to its very low consumption: precisely because of this characteristic, combined with the low cost of Bluetooth devices, it was decided to take advantage of this technology. The devices that make up the indoor localization system communicate with each other via Bluetooth connection, providing the necessary data to be able to calculate the coordinates of the position later on. The main advantages, however, can be summarized in three points:  
* Complete absence of cables and wires: Bluetooth allows, in fact, direct communication between various devices without the need for further connections;
* Limited cost;  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Method** & **Benefit** & **Downside** \\ \hline ToA & It represents the most accurate technique in terms of precision & It is complex to implement; requires synchronization of all devices; expensive \\ \hline TDoA & Compared to the ToA, it requires the synchronism of the reference devices only & It is affected by multipath phenomena \\ \hline AOA & The transmitter timing information is encoded in the signal & It requires the use of additional antennas to measure angles and therefore has a higher cost; multipath and reflection phenomenon \\ \hline RSS & Very simple to implement; it does not require synchronization between devices; it requires no additional hardware & The presence of obstacles, the orientation of the antennas and the environment make it difficult to create an accurate model of indoor localization \\ \hline \hline \end{tabular}
\end{table}
Table 2: Advantages and disadvantages of indoor localization algorithms.  
* Complete automation. The Bluetooth standard can be divided into three types of classes, each of which have a different range, as shown in Table 3.  
As can be seen from the table, this technology can reach an action range of up to 100 m, thus making it very useful in an indoor environment. As regards the estimation of the position, Bluetooth is exploited using a system consisting essentially of a Bluetooth module that acts as a detector (in slave mode) and other devices (set in master mode) called beacons of which the location in the area of interest. The position estimation can be determined starting from the signal strength that each master device detects from slave devices. The main advantage of this technology, as previously mentioned, depends both on the low power consumption, but also on the easy availability of hardware; most of the devices available on the market today, such as smartphones, tablets and computers, integrate within them already the Bluetooth standard [29; 30]. The disadvantage, on the other hand, is the countless interferences that the system can suffer. In a very small and limited area, any type of obstacle, whether it is a person or any other device, can limit and therefore decrease the accuracy when measuring the signal strength. This limit translates into an estimate of the wrong, or at least different from the actual, position [31].