## 5 Conclusions
Some criteria must be stringently met in future approaches, such as the ability to adapt to numerous positions of the user, the heterogeneity of transmitters and receivers, and the consumption of energy. Adaptability to indoor positioning: The most adherent algorithms and technologies (acceptance by those who use them to build systems and by those who use the final product) are those that allow their application with a higher rate of adaptation. For example, portable systems can be offered for applications on smartphones and other devices that can be used in various positions on a person, such as in a pocket, purse, or the user's hand, fixed at the height of the head, etc. Heterogeneity: In an indoor location and an indoor navigation application for the visually impaired that is intended to be made available to large masses of users, the hardware and algorithms must be able to deal with the various characteristics of closed environments. Multiple wearable devices, such as smartwatches, smartphones, and the countless gadgets presented in recent years, can be used to provide different sensitivities and data patterns. Power consumption: It is known that battery life on many commercial smartphones is not as good as desired. The same is true of other wearable devices. Therefore, it is crucial to develop new algorithms that are energy-efficient, with reduced computational complexity. In several works described in this review, we note the efforts of the authors to solve problems of location in indoor environments. They deal with different characteristics that interfere with the signals and data received by the sensors and try to take advantage of the technologies and techniques already consolidated for the external environment. This means that, although current studies are looking for a model for indoor environments, in the future, the solutions will be more comprehensive and will be integrated with indoor or outdoor location services as they become available. Other problems related to the global positioning models (external and indoor) that require attention are privacy and security. In this research, few authors have identified the need to preserve information about the user's location during the experiment, such as [PERSON] et al. and [PERSON] et al. [13; 134]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Technology** & **Precision** & **Weaknesses** \\ \hline TDoA.1  & 1.34-1.50 m & Infrastructure \\ RSSI 2  & 1.80-6.00 m & Low Precision, access point \\ RSSI 3  & 2.40 m & Infrastructure \\ RFID 4  & 0.32 m & Very low precision \\ ZigBee & 0.25 m & Special equipment \\ Audio & 1.30 m & Sensitive to audio noise \\ Ultrasonic & 1.00 m & Infrastructure \\ Ultrasonic with TDoA 1  & 0.35 m & Infrastructure \\ VLC 5  & 0.20-0.23 m & Infrastructure \\ Fixed camera & 0.10 m & Sensitive to light conditions \\ Mobile camera & 0.20 m & Sensitive to light conditions \\ VLC 5/WiFi—inertial sensor & 0.23 m & Infrastructure \\ Inertial & 0.30-2.50 m & Sensitive to the presence of metallic materials and people \\ Inertial with camera & 0.50 m & Sensitive to light conditions \\ W-Fi with inertial & 1.35-4.00 m & Sensitive to the presence of metallic materials, people, and focusing signals by the infrastructure \\ Wi-Fi with cameras & 0.20 m & Sensitive to light conditions \\ Infrared with camera & 0.70 m & Sunlight, sensitive to light conditions \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of leading indoor positioning technologies. Other authors treated security as an essential item for users and observed that its application may or may not influence the decision to adopt a location system [9; 81]. Although privacy has been a concern since the beginning of the development of IPSs, it is understandable that the matter now is to define the best algorithms and technologies in the future, and this will be one of the primary considerations for the adoption or choice of specific IPSs. The individual contributions for each author were as follows: conceptualization, methodology: W.C.S.S.S., N.J., and V.F.d.L.J.