## 5 Conclusions  
This work researched indoor positioning systems (IPSs), with a focus on those that can be applied in the tasks of locating and assisting with the indoor navigation of visually impaired people. A general classification of IPSs was carried out. Each selected group was reviewed, analyzing the advantages and disadvantages of the systems in terms of precision and scalability. Then, hybrid systems were evaluated with a focus on current solutions available in the literature. All solutions were also analyzed for their use on mobile devices, especially on smartphones, as these devices are popular worldwide and have the advantage of having most of the sensors used in IPSs, which reduces the cost of mass deployment of an IPS. Considering the requirements in building applications for the visually impaired, which require high levels of accuracy, information delivery time, and scalability, it is possible to observe that in the literature, the approaches described as hybrid enrich the information generated by the algorithms. Hybrid arrangements can create more reliable or complementary information so that some data can cover the deficiencies of others in specific locations. It is essential to point out that today, smartphones already have several built-in technologies, such as Wi-Fi, Bluetooth, BLE, IMU sensor, and an increasing number of high-definition cameras, which can be added to mapping and location schemes to increase system accuracy. Current technologies have shown significant advances in terms of accuracy and speed and have been used in new algorithmic arrangements to improve the quality of internal positioning systems. However, the problem of positioning in indoor environments is far from being solved, and it needs further research to obtain the accuracy required by certain types of users, such as visually impaired people. Besides, in the case of indoor positioning systems based on technologies that use special-purpose devices and specialized infrastructure (for example, sensor networks, readers, and encoders), the cost of acquisition, installation, and maintenance is high. Transmitting this high-cost perception to the end-user, in many cases, makes its acceptance unfeasible. There is still no satisfactory solution to the problem of an IPS capable of being used in all indoor scenarios with standard behavior. Fully accurate solutions are costly, or they are not in real time, or cheaper proposals are very inaccurate. \begin{table}
\begin{tabular}{c c c c c} \hline
**System** & **Type** & **Solability** & **Limitations** & **Error Value** \\ \hline [PERSON] et al. [4] & TDA\({}^{1}\) & Limited & Time & 13.4m \\ [PERSON] et al. [4] & RSSI [78082] & No & Does not identify the direction & 2.0m \\ [PERSON] et al. [20] & Audio & Limited & Noise & 1.30m \\ [PERSON] et al. [4] & Ulluosen-Miller & Unimod & Limited & Live & 0.35-10.0m \\ [PERSON] et al. [9] & ULC & & Limited & 0.02m (0.24m) \\ [PERSON] et al. [10] & Field &  
In practice, the evolution of technologies and algorithms has had an incredibly positive impact on the growth of indoor positioning systems. Changes in new technologies have given software designers greater freedom to experiment with new approaches that were previously nonviable due to their limitations. Also, new technologies offer the opportunity to close gaps in the research and can be used alone or combined with other, already tried models. The details of the technology, technique, and implementation affect the accuracy of the system. For example, [PERSON] and [PERSON] used internal positioning based on triangulation [58; 133]. [PERSON] used Bluetooth and had an average error of 2.08 m, while [PERSON] used VLC and indicated a much lower margin of error, with about 0.10 m in the tests. Based on the comprehensive review of the literature, this research can encourage new research efforts, and for this reason, we suggest here some lines of future research in this area.