# Precise Positioning of Autonomous Vehicles Combining UWB Ranging Estimations with On-Board Sensors
## 6 Conclusions  
Today's society is undergoing continuous technological changes that seek to improve the actual quality of life and work. As a result of these changes, the vehicle manufacturers and governments are putting a lot of effort in the development of autonomous vehicles to increase road safety and vehicle's  
Figure 16: Accumulative distribution function of the UWB and the odometry and IMU positioning error. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Pos.System** & \(\mathbf{\mu_{\epsilon_{p}}}\) & \(\mathbf{\hat{\sigma}_{\epsilon_{p}}}\) & \(\mathbf{\widehat{RMSE}_{\epsilon_{p}}}\) & \(\mathbf{\epsilon_{p}}\) & \(\mathbf{Max(\epsilon_{p})}\) \\ \hline IMU-Odometry & 205 cm & 142.8 cm & 249.8 cm & 407.3 cm & 410.6 cm \\ UWB-IMU-Odometry (raw) & 36.1 cm & 20.2 cm & 41.4 cm & 61.4 cm & 173.4 cm \\ UWB-IMU-Odometry (processed) & 17.2 cm & 7.1 cm & 18.6 cm & 27.1 cm & 46 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistical analysis of the positioning distance error \(\epsilon_{p}\)efficiency. For having an optimal performance, an autonomous vehicle needs to have, among other things, a continuous knowledge of its exact location on the road. As it has been recalled, this issue has been traditionally covered by GNSS signals in combination with on-board data of the vehicle. This data fusion provides an accurate, high rate and reliable position of the vehicle under good GNSS conditions, in other words, when the vehicle's GNSS receiver can track at least four GNSS satellites. However, this is not always possible, as there are certain environments in where GNSS signal reception is limited or impossible due to numerous obstacles that block the signals. In these areas, the vehicle's position is computed directly from its on-board data. The problem of these data when used alone is that they have a tendency to drift with time leading to an inaccurate and unreliable position. Therefore, if the GNSS signal reception is affected over long periods, the position provided by this data fusion will be extremely inaccurate, making necessary the use of an alternative positioning system. One of the technologies which can be postulated as a candidate in those areas with no GNSS coverage is the UWB technology. In the last years, much effort has been devoted to study the potential of this technology, specially, in indoor applications. In our research we intended to evaluate a less-studied aspect of this technology, the use of UWB ranging estimates to track the vehicle's position in an outdoor environment. The main idea of this work has been to build an accurate and reliable positioning solution based on the combination of UWB ranging estimates together with inertial and odometry data of the vehicle. This study has been characterised inside the scope of the PRoPART project and has made use of a customised UWB ranging system and a RC car as testing vehicle. Meaning that, the used setup has been determined for validating the UWB ranging system in terms of accuracy, coverage and continuity in the PRoPART solution. In addition, our proposal includes an UWB tag in which the antenna is physically separated from the UWB module by making use of an external antenna connected through a cable. This innovative proposal allows to have a flexible solution which can be adapted accordingly to the application without compromising the accuracy. The proposed positioning solution based on a EKF has been tested by carrying out simulations and real tests. On the one hand, the simulations have allowed us to better understand the performance of the positioning algorithm. On the other hand, the real tests carried out in AstaZero proving ground have proved the enhancement of the RC car positioning when using UWB measurements for correcting the position computed from the RC car on-board data. The obtained results show a RMSE of the positioning distance error over the whole trajectory of 18.56 cm, being the maximum positioning distance error of 46 cm.