# A Review of Wireless Positioning Techniques and Technologies: From Smart Sensors to 6G
###### Abstract  
In recent years, tremendous advances have been made in the design and applications of wireless networks and embedded sensors. The combination of sophisticated sensors with wireless communication has introduced new applications, which can simplify humans' daily activities, increase independence, and improve quality of life. Although numerous positioning techniques and wireless technologies have been introduced over the last few decades, there is still a need for improvements, in terms of efficiency, accuracy, and performance for the various applications. Localization importance increased even more recently, due to the coronavirus pandemic, which made people spend more time indoors. Improvements can be achieved by integrating sensor fusion and combining various wireless technologies for taking advantage of their individual strengths. Integrated sensing is also envisaged in the coming technologies, such as 6G. The primary aim of this review article is to discuss and evaluate the different wireless positioning techniques and technologies available for both indoor and outdoor localization. This, in combination with the analysis of the various discussed methods, including active and passive positioning, SLAM, PDR, integrated sensing, and sensor fusion, will pave the way for designing the future wireless positioning systems.  
localization techniques; positioning algorithms; range-free; range-based; tracking techniques; wireless technologies for positioning +
Footnote †: journal: _Signals_  
of specific phenomena or events. WSNs typically consist of a large number of small-in-size sensor nodes with low power consumption and are envisioned for a variety of applications, including fire detection, crop quality monitoring, field surveying, health-related applications (i.e, listing of patients, doctors and supplies, staff and patient tracking, and elderly care), commercial applications (i.e., inventory control and products' tracking), and military applications (i.e., soldier and mines tracking). The localization and tracking capability is an important aspect of WSNs, since the knowledge of the sensor location is needed to make the collected data meaningful for the various applications. Additionally, the Internet of Things (IoT) digitization and datafication, together with the integration of smart devices, made localization of vital importance.  
Generally, localization or positioning determines the position of a node by utilizing techniques and wireless technologies characteristics. To achieve that, some transmitting or receiving nodes with known coordinates are required, referred to as \"anchors\", \"beacons\", \"reference nodes\", \"base stations\", or \"access points\". Similarly, the nodes with the unknown coordinates that need to be localized are referred to as \"targets\", \"mobile nodes\", or \"stations\", and they can be either the transmitting or receiving nodes. Commonly, the names are associated with the particular wireless technology used. Throughout the present work, the nodes with known coordinates will be referred to as \"transmitting nodes\" and the ones with unknown locations as \"receiving nodes\".