# A Survey of Visible-Light-Communication-Based Indoor Positioning Systems
## 3 Technologies for Indoor Positioning Systems
### Other Methods  
Apart from the widely used positioning method named GPS, which is the most discussed in Section 1, there are a variety of alternative solutions [40]. These alternative methods and their performance can be evaluated and analyzed by referring to the relevant literature [40] and corresponding references. When considering positioning systems, it is crucial to take into account various criteria and considerations, such as accuracy, cost, information requirements, computational complexity, and user privacy. For further discussion, readers are encouraged to explore the details presented in [41]. Table 1 presents a comprehensive overview of the major positioning methods, highlighting their accuracy and cost in parallel with VLC-based IPSs. Subsequent discussions will delve into the specifics of each method.  
Figure 2: Example of a VLC indoor positioning system: Epsilon [14].  
Cellular-based positioning systems are more commonly used outdoors than indoors. Similar to GPS, a mobile user uses signals received from base stations to determine its own position. In addition, base stations can also use signals received from mobile users and combine them at a central coordinator to estimate the mobile's position [42]. The positioning accuracy in these systems is affected by factors such as the density of base stations and the positioning methods, including received signal strength (RSS), angle of arrival (AOA), time of arrival (TOA), or a combination of these. It is important to note that sources of positioning error include non-line-of-sight (NLOS) propagation, multipath propagation, and multiple access interference. Despite the progress that has been made, there are still several technical challenges that must be overcome to achieve accurate positioning.  
Wi-Fi-based positioning systems typically involve adding a location server to an existing WLAN infrastructure. These systems use methods such as RSS or fingerprinting for positioning measurements [43], and further discussion can be found in the references therein. In order to implement Wi-Fi-based positioning systems, centralized entities such as fingerprint databases of Wi-Fi signals are required. Therefore, site measurement of Wi-Fi signals to build the database is inevitable during initial deployment or when relocating access points (APs), but it is labor-intensive and time-consuming. Regarding RFID systems [44; 45; 46], passive RFID cards are unable to provide detailed high-resolution localization within a room. On the other hand, active RFID cards are more practical for indoor positioning systems because they regularly transmit signals to receivers in a given area, enabling positioning. However, these systems often have slow response times and relatively long latency compared to other methods.  
Both infrared (IR)- and Bluetooth-based systems are designed for short-range, low-power communications. As a result, they are not well suited for user mobility and accurate positioning. An exploration of hybrid Wi-Fi and Bluetooth systems for indoor positioning can be found in [47]. UWB- or ultrasound-based systems can provide high positioning accuracy, but their cost is significantly higher than other alternatives. In contrast to other positioning systems, VLC-based systems have several advantages. First, the accuracy of VLC systems meets the requirements of high-resolution indoor localization while keeping costs low because of the existing lighting infrastructure. In addition, VLC systems use the license-free visible light spectrum, eliminating the need for additional licenses. Second, VLC-based systems are environmentally friendly because they use energy-efficient LEDs as transmitters, resulting in low power consumption and minimal radio frequency interference.