# Using Deep Learning for Collecting Data about Museum Visitor Behavior
## 2 State of the Art
### Indoor Localization Technologies  
In the following, we report the most used technologies for indoor tracking. * WiFi. This technology is extensively used for network connection of various devices in public and private environments. Initially, its maximum coverage was about 100 m, today it has been extended to over 1 km with the IEEE 802.11 ah protocol, published in 2017, specifically designed for Internet of Things (IoT) services [20]. The fact that it is supported by almost all the electronic devices on the market makes it one of the most used technologies for indoor localization, without the need for additional infrastructure. However, its characteristics of wide coverage and high throughput yield to a more suitable usage for communication than localization, because of its low accuracy and interference, which make it necessary to use complex processing algorithms. * Bluetooth. This technology is used for wireless connection between mobile and fixed devices within relatively small distances. The latest version, called Bluetooth Low Energy (BLE), provides improved performance in terms of coverage and throughput, with low power consumption [21]. Recently, two BLE-based protocols have been proposed: Eddystone (by Google Inc.) and iBeacons (by Apple Inc.). They are intended more for proximity-based services than localization, due to poor accuracy and high sensitivity to noise. * Infrared. Among others, the IR technology was the first one to be widely used in many projects (e.g., see [8; 22]). However, it has several limitations [23]. Firstly, it requires the presence of visible IR emitters and a line of sight between the emitter and receiver. Lastly, the nature of the IR signal requires accurate calibration of the parameters of the IR emitters and the active involvement of visitors in the process of locating their position. * Radio-Frequency Identification. This technology is used to transfer data between a reader and a tag capable of communicating on default radio frequency [24]. There are two types of RFID systems: Active and passive. The first one operates with microwave and Ultra High Frequency (UHF) ranges, and it is characterized by low cost and ease of integration into the objects to be tracked. However, their low accuracy and poor integration in portable devices make them unsuitable for indoor location purposes. Passive RFID systems can operate without a battery but have significant limits in terms of coverage, which makes them unsuitable for indoor location purposes. * IEEE 802.15.4. This technology is mostly used in wireless sensor networks and is characterized by good energy efficiency, low cost, but also by low throughput [25]. This standard is not available on most devices on the market and for this particular reason, it is not suitable for the indoor localization of users. * Ultra Wideband. This technology is mainly used in short-distance communication systems and is characterized by low energy consumption [14]. The main characteristics of the UWB technology are the robustness to interference and the possibility to penetrate various materials. For these reasons, it is extremely suitable for indoor localization. However, due to its limited implementation in portable devices, it cannot be widely used. The UWB problems have been extensively analyzed by the authors of [26] and in practical scenarios, the Non-Line-of-Sight (NLOS) propagation can be the main issue of this technology. * Visible Light. Indoor localization technology based on visible light can be realized using different types of sensors. The most common are Light-Emitting Diodes (LEDs) [27]. The use of LEDs for indoor localization has numerous advantages over other technologies. First of all, emitters and sensors are very popular considering their low cost. They are also resistant to changes in humidity and they have low energy consumption. The main disadvantage of LEDs is that a line of sight between them is required [18]. Another type of sensor used in visible light systems is Light Detection and Ranging Localization (LIDAR).