## 3 5G Technology Enablers for V2X Use Cases
### Positioning Capabilities of 5G and Enablers
#### 3.3.3 Cooperative localization  
In a significant proportion of cases, vehicles are surrounded by other vehicles (urban situations, highway traffic), so the possibility of cooperation appears to further improve the localization predictions. Ref. [33] summarizes the main aspects and advantages of cooperative localization. The paper lays the foundations for handling these methods and gives evaluation and comparison criteria. One of the most important requirements for cooperative localization to work effectively is to have enough vehicles on the road using these technologies. As (semi-)autonomous vehicles are not widespread enough at the moment, the development and evaluation of these technologies are based on simulations rather than real-life data. Because the development and research of these technologies are still in an early stage, current research papers propose different approaches and focus on one special aspect of this topic rather than providing a complete solution. Ref. [47] presents one possible cooperative positioning and mapping method. It handles multi-path signals induced by the environment as a resource by creating a radio map and compares two different approaches. In [40], a different method is proposed, which can handle the challenges of the mapping and vehicle state estimation by using radio mapping based on large antenna arrays. The proposed algorithms exploit all available signal paths using a multi-model PHD (probability hypothesis density) filter and a map fusion routine. Research regarding cooperative positioning is also present in other areas, e.g., industrial mobile networks, the results of which can also be utilized in vehicle-to-vehicle cooperative positioning. For example, seamless positioning using cooperation between \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Technologies** & **Main Approach** & **Methods** & **Results** & **Comment** & **Ref.** \\ \hline IMU—5G & edge computing & EKF for fusing the estimation results & a simulation environment for scene generation, signal propagation, and position estimation & submeter accuracy, the effect of the number of base stations tested & [38] \\ \hline SLAM—5G & intermediate approach & end-to-end processing & problem decomposition & mapping and vehicle estimation & matching \\  & (the wave is not directly mapped to the position) & end-to-end processing & with real channel estimation & simultaneously, accurate estimated number, type, and position of landmarks & [48] \\ \hline GNSS—5G & newly proposed method: crossover multiple-way & \begin{tabular}{c} D2D range and angle measurements, measurements, integrated algorithms, state dimension \\ reduction \\ \end{tabular} & \
\begin{tabular}{c} fewer communication \\ resources needed \\ \end{tabular} &
\begin{tabular}{c} less computation \\ without losing \\ information, accurate \\ and robust method \\ \end{tabular} & [49] \\ \hline GNSS—5G & physical-layer & urban macro-cell & & 5 m horizontal \\  & abstraction-based & environments, & different GNSS & accuracy in 95\% of \\  & simulation, WLS & Gaussian-distributed & constellations examined & cases in not ideal conditions (AV, UC) \\  & algorithm & error model, CDF & & \\ \hline GNSS—5G & visibility mask handling & evaluation: CRB, FIM, & simulation framework & NLOS signals have to \\  & cmWave and mmWave & number of base stations, & presented to test typical & be weighted, \\  & signals & CDF & urban scenarios & submeter accuracy \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison table for hybrid localization technologies. The respective abbreviations are the following: inertial measurement unit (IMU), simultaneous localization and mapping (SLAM), Poisson multi-Bernoulli mixture (PMBM), device-to-device (D2D), cumulative density function (CDF), asymmetric visibility (AC), urban canyons (UC), Cramer–Rao bound (CRB), Fisher information matrix (FIM), weighted least squares (WLS). mobile terminals (MTs) is presented in [46].