## 2 Related Work  
The research area dealing with indoor positioning systems has received many contributions in recent years. Although many products are already available for use, this is a topic still considered open for discussion. Even the most modern approaches need updates due to the evolution of hardware and interventions in the mathematical models that define the construction of the algorithms, as widely described by authors such as [PERSON] et al., [PERSON] et al., [PERSON] et al., [PERSON] et al., [PERSON] et al., and [PERSON] et al. [10; 15; 16; 17; 18; 19]. Another issue described in several studies is the need to establish clear objectives, which can be achieved by experimentation and allow replication, attracting more interest from those who seek to develop criteria for the construction and evaluation of projects. The requirements identified as feasible to be met and proven are precision, speed, and a balance between the two factors [20]. For example, [PERSON] et al. described the concern to find a balance between maintaining a high level of accuracy without affecting the delivery time of information to visually impaired users when using internal navigation systems [21]. The list of works selected for the construction of this research mainly covers those that discriminate their technological and technical approaches. The works cited in this paper are concentrated in the period 2011 to 2020. Particular attention is paid to the period after 2015. Our goal is to highlight a more current view of where the advances in the area are located. Two investigation profiles allow the construction of this review: review-type works and applied works (journals, papers). Review-type works indicate research organization strategies that other authors have prepared, and other works (excluding reviews) are used to show the results achieved in practice using the technological and technical approaches presented in the reports. This research presents the strategies that use specific technologies and methods that combine different hardware and algorithms to compose hybrid arrangements, which seek greater precision robustness, error control, and response time, as described by [PERSON] and [PERSON] [16; 22]. The subject is quite comprehensive when discussing the composition of models, systems, and objectives [23]. Although the use of such systems allows the location, tracking, and navigation of targets in internal environments, their construction processes are established to meet precision and punctuality requirements defined jointly by the users responsible for the development of the system and the limits set by the hardware and software layers [24]. In general, fast applications use simple algorithms that ignore variables and some processes and require less processing and memory usage [25; 26]. More complex applications provide more complete data, and therefore more accurate systems; however, they need more time to perform their calculations [2; 27]. Applying more simplified algorithm formulations linearizes the problems and can deliver results more quickly, within tolerable limits of variation of results, as indicated by [PERSON] and [PERSON] [15; 28]. Complex algorithms are justified by the deepening of knowledge about the data, requiring more time to separate essential data from data that contribute little or indicate redundancy of information, as reported by [PERSON] and [PERSON] [29; 30]. Some authors use hybrid approaches that find a balance between the two variables [16; 31]. Knowing the classes of logical formulations, as well as associated techniques and technologies, is an essential requirement for researchers to define their IPS projects. Some authors establish criteria for organizing their surveys to describe the standards adopted in indoor location and navigation projects. In these criteria, sometimes authors choose to group techniques and technologies, and sometimes they go into more detail, always focusing on the final reader and accelerating the understanding of the resources available for their research.