# OBU for Accurate Navigation through Sensor Fusion in the Framework of the EMERGE Project
## 3 Sensor Fusion: Loosely Coupled Algorithm Implementation
### The Initialisation Loop
The purpose of this experimental setup is to evaluate each subsystem and check the individual performances of each sensor. The test also covers the process of interconnection, configuration, decoding, and calibration of the sensors involved. The verification process of the GNSS system (GNSS Antenna + SIRIUS ROVER: ZED-F9P) is a comprehensive series of experimental tests where all the components of the GNSS subsystem are thoroughly evaluated: the antenna, the communication interfaces, the SW block dedicated to decoding, as well as the performances in terms of position calculation (PVT). Furthermore, the impact of the PointPerfect (Augmentation service) is evaluated. Table 1 shows some performance results that cover the cases of using the GPS and Galileo constellations without PointPerfect service and the case of using the full capability of the GNSS receiver (GNSS + PointPerfect augmentation service). The reference system (known positions) used in the performance calculations was derived from previous long-term PPP-RTK measurements. The inertial measurement system (Xsens--MTi 630 AHRS) is also verified in a stationary scenario. In addition to validating the interfaces, configuration, and SW components dedicated to coding/decoding, this process allows the creation of a data set that was used to characterise the inertial error in the GNSS + IMU integration process. ### Sensors Verification

Before a complete and definitive test of the OBU in a real environment, we present a verification of the performance of some fundamental system elements. Particular interest falls on the satellite navigation system, which includes two fundamental components: the GNSS multi-constellation/multi-frequency receiver and the Augmentation Service, which \begin{table}
\begin{tabular}{c c c c} \hline \hline
**KPI 1** & **Parameters** & **GPS + GALILEO [\(\mu\), \(\sigma\)]** & **GNSS and PointPerfect [\(\mu\), \(\sigma\)]** \\ \hline Accuracy & 3D Position [m] & 2.26, 0.52 & 0.10, 0.25 \\  & Horizontal Position [m] & 1.70, 0.44 & 0.06, 0.18 \\  & Vertical Position [m] & 1.46, 0.41 & 0.08, 0.18 \\ \hline Availability and Continuity & SVs Used [U] & 11, 2 & 26, 2 \\  & SVs Tracked [U] & 24, 3 & 36, 3 \\  & SVs Received [U] & 28, 3 & 37, 3 \\  & C/N0 [dB-Hz] & 36.47, 1.5 & 34.31, 1.3 \\  & GDOP & 2.3, 0.6 & 1.7, 0.2 \\  & HDOP & 1.3, 0.5 & 0.8, 0.13 \\  & VDOP & 1.4, 0.4 & 1.2, 0.2 \\ \hline Integrity & North Protection Level [m] & 8.86, 4.69 & 2.09, 5.59 \\  & East Protection Level [m] & 10.93, 6.61 & 2.44, 6.03 \\  & Down Protection Level [m] & 11.75, 6.41 & 4.08, 7.48 \\ \hline TTFF & TTFF 2 [s] & 28.75, 1.71 & 26.34, 1.33 \\ \hline Other performance parameters & 3D Velocity Error [m/s] & 0.26, 0.09 & 0.13 0.03 \\  & Time Accuracy [ns] & 0.0036, 0.0009 & 0.0011, 0.0009 \\  & TDOP & 1.1, 0.3 & 0.8, 0.1 \\ \hline \hline \end{tabular}

* This table groups together the information collected that could provide answers to the KPIs organised in the first column. In the last years, some constellations have defined specific KPIs and parameters, so note that the parameters shown are only a portion of these. 2 TTFF is time elapsed between a _collstart_ and a valid _Fix_ detected in the GNSS receiver.

\begin{tabular}{c c c c} \hline \hline  & & & \\ \hline GNSS Antenna + SIRIUS ROVER: ZED-F9P & Interface Handler & Test & Output \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline \end{tabular}

* PVT values using different combination of GNSS constellation
* TTFF, Accuracy, Integrity

\end{table} 
Table 1: Experimental results of the satellite navigation module with two different configurations: using two GNSS constellations (GPS + GALILEO) and the GNSS (all constellations) integrated with the PointPerfect Augmentation service (GNSS + PointPerfect). For each parameter, \(\mu\) and \(\sigma\) denote statistical mean and standard deviation, respectively. Figure 6: Experimental setup for sensor verification tests.