# A Review of Wireless Positioning Techniques and Technologies: From Smart Sensors to 6G
## 4 Discussion
### Future Directions
#### 4.3.4 From Smart Sensors to 6G  
Sixth generation wireless (6G), the successor to 5G cellular technology, is a promising technology for providing an arena of new service capabilities with positioning and sensing to be part of the wireless communications, in addition to the the incorporation of artificial intelligence (AI) and machine learning (ML). The AI and ML can improve the data processing, especially for system models that are difficult to design and solve. In addition, they provide feature extraction and motion modelling algorithms for tracking augmented reality (AR) and extended reality (XR) objects in the scene and estimating their location and orientation [134; 138]. In particular, AR provides additional digital elements to the surroundings by utilizing the smart devices' camera and virtual reality (VR), which replaces the real environment with a simulated one, while XR provides the experience of being physically and spatially located in a virtual environment. The autonomous navigation and localization will be provided with augmented human and computer vision in NLoS imaging.  
The evolutionary trend of 5G towards high frequency ranges, wider bandwidth, and massive antenna arrays deployment is intended to continue into the sub-Terahertz region (0.3-3 THz) in the 6G systems [139]. The sub-THz communications requires the deployment of extreme massive MIMO antennas [138]. The short wavelengths at THz can provide massive spatial multiplexing communications, accurate sensing, imaging, and spectroscopy [134]. The sensing applications include air quality monitoring, gesture recognition, explosives' detection, and gas sensing, as well as centimeter-level positioning [134].  
The wireless devices equipped with 6G will gather information from different locations in an effort to create detailed 3D maps of the world, thus providing positioning, as well as mapping and sensing services. For instance, SLAM will not require prior knowledge of the environment [140]. Additionally, certain materials and gases that have vibrational absorption at particular frequencies throughout the THz band will be detected through the frequency scanning spectroscopy; so, the smart devices equipped with 6G will be capable of sensing certain chemicals and defects in the environment [134]. Furthermore, the provided \(\upmu\)Wave frequencies [139] are expected to reach shorter distances with smaller beam widths, thus providing higher positioning accuracy.  
The high-resolution sensing is also an integral part of the 6G systems. In addition, in the 5G new radio (NR) positioning, 6G carrier aggregation will be effectively used for combining the position reference signal (PRS) to a single signal and eliminating the various limitations associated with signal strength, time-based, and angle-based measurements (i.e., the signal strength accuracy depends on path loss--the time-based is limited by the bandwidth of the PRS aid and the angle-based accuracy is limited by the antenna array or aperture) [138]. In general, the 6G includes numerous promising features with the potential of merging imaging and communications for precise positioning.