# A Review of Wireless Positioning Techniques and Technologies: From Smart Sensors to 6G
## 3 Wireless Technologies
### Cellular
#### 3.2.3 Fifth Generation (5G)  
The fifth generation (5G) is the latest established global cellular technology. It aims to introduce advanced key technologies with much higher system capacity, spectrum efficiency, energy efficiency, and transmission data rates. It also aims to address the different limitations of previous generations and be a potential key enabler for future IoT. Moreover, it aims to improve the positioning, with the ultimate goal of providing 6D positioning, i.e., 3D spatial location with roll, pitch, and yaw positioning, which is needed for virtual and augmented reality technologies [10]. The prerequisite is for the receiving node to be equipped with an antenna array, so that both AoA and AoD can be estimated simultaneously in either the uplink or the downlink modes [78]. The 5G utilizes high directional antenna arrays with narrow and wide bandwidths for more accurate localization. It also utilizes the mmWave frequency band with large antenna array deployment at both ends. Although the mmWave frequency band suffers from higher path loss in the first meter of propagation and greater blockage, it is expected to achieve a positioning accuracy of less than 1m for indoors and dense urban areas, due to the ultra-wide bandwidths available [79]. The mmWave and THz bands are affected by the weather conditions. In [80], the mmWave and THz bands wireless link budgets were evaluated under extreme weather conditions, such as storms, which include a combination of high temperature, violent rain, and strong winds. It was found that only the 400 GHz carrier was relatively sensitive to severe wind effects, while the link performance was affected regardless of the carrier frequency. Furthermore, the narrower half-power beamwidth (HPBW) of the antenna arrays allows the AoA of the received signals to be estimated precisely. A finer time resolution of the multipath signals is also provided by the large bandwidths [9]. Moreover, the multi-user _multi-input multi-output (MIMO)_ technologies, shown in Figure 14, are utilized in 5G. They are based on information theory and utilize the properties of an imperfect CSI, as well as AoA estimations for precise signal orientation. MIMO provides the opportunity for exploring the multipath by performing mapping and synchronization [79]. For instance, in [81], numerous snapshots were collected from each base station (BS) and were processed for estimating the location of the unknown receiving node by using the AoA of the LoS paths, under the assumption that there is a LoS path for each BS. Additionally, the massive antenna deployment is included in the 5G technology, which increases the signal strength without changing the radiated power [75]. In [78], an algorithm was developed for coherent passive localization in massive MIMO systems with distributed phased antenna arrays, aiming to solve the ambiguity problem inherent to coherent position estimation. The 5G technology aims to also provide _massive machine-type communications (mMTC)_, which are predicted to reach tens of billions of connected heterogeneous devices, such as actuators and sensors [10]. The device-to-device (D2D) communication is also introduced in 5G, enabling receiving devices for direct communication with one another and achieving localization of all the receiving devices. Another key network enabler is the cognitive radio (CR) technology, which utilizes the limited and scarce spectrum resources for supporting the high demand of new services requirements of emerging and promising IoT applications. The CR understands the context in which it is located and can tailor the communication process; thus, it is fully aware of the context in which it operates. It is a self-organizing system, in terms of dynamic spectrum access, beam pattern, routing algorithms, coding, and filtering techniques, and aims to reduce the manual configuration and, in turn, provide lower costs. It may be the next generation of cellular networks [10].