Inside GNSS Media & Research

JUL-AUG 2019

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www.insidegnss.com J U L Y / A U G U S T 2 0 1 9 Inside GNSS 63 results with which the STAN naviga- tion framework was compared. e experimental setup is shown in Figure 19. e ground vehicle was driven along U.S. Interstate 5 near Irvine, California, USA, for 7,495 meters in 258 seconds, dur- ing which 2 Orbcomm LEO satellites were available (FM 112 and FM 117). Figure 20(a) depicts a skyplot of the satellite trajectories over the course of the experi- ment. Figure 20(b) shows the Doppler measured by the MATRIX SDR and the estimated Doppler using satellite position and velocity obtained from TLE fi les and an SGP4 propagator for the 2 Orbcomm satellites. To estimate the UAV's trajectory, 2 nav- igation frameworks were implemented to estimate the ground vehicle's trajectory: (i) the LEO-aided INS STAN framework and (ii) a traditional GPS-aided INS for comparative analysis. Each framework had access to GPS for only the fi rst 30 sec- onds. Figure 21(a) illustrate the trajectory the 2 Orbcomm LEO satellites traversed over the course of the experiment, Figure 21(b)-(c) illustrate the ground vehicle's true trajectory and those estimated by each of the 2 frameworks, and Figure 21(d) illustrates the estimated trajectories of one of the Orbcomm satellites as well as the fi nal 95-th percentile uncertainty ellipsoid (the axes denote the radial (ra) and along-track (at) directions). Table 4 summarizes the final error and position RMSE achieved by each framework a er GPS cutoff . A. UAV NAVIGATION An experiment was conducted to evalu- ate the performance of the LEO-aided INS STAN framework on a UAV. To this end, the UAV was equipped with the fol- lowing hardware and so ware setup: • A high-end quadrifi lar helix antenna • A USRP to sample Orbcomm signals. ese samples were then processed by the Orbcomm receiver module of the MATRIX SDR. Unaided INS LEO-aided INS STAN Final Error (m) 3,729.4 192.3 RMSE (m) 1,419.3 416.5 Table 4: Experimental results with 2 Orbcomm LEO satellites for a ground vehicle navigating about 7.5 km in 258 seconds (GPS signals were cut off after the fi rst 30 seconds). These results are after GPS cutoff . FIGURE 21 Results of the ground vehicle experiment. (a) Orbcomm satellite trajectories. (b)-(c) Ground vehicle true and estimated trajectories. (d) Estimated trajectory and the fi nal 95-th percentile uncertainty ellipsoid for one of the Orbcomm satellites. Map data: Google Earth. FIGURE 22 Hardware and software setup for the UAV experiment. • A consumer-grade MEMS IMU, which is proprietary hardware of the UAV manufacturer and used in its f light controller. Log fi les were downloaded from the drone to parse the raw IMU data, which were subsequently fed to the INS of the STAN framework. • A pressure altimeter, which is also pro- prietary hardware of the UAV manu- facturer and used in its fl ight control- ler. Log fi les were downloaded from the drone to parse the altitude measure- ments, which were subsequently fed to the EKF of the STAN framework. e ground truth trajectory was taken from the UAV's onboard navigation sys- tem, which consists of a MEMS IMU, a multi-constellation GNSS receiver (GPS and GLONASS), a pressure altimeter, and a magnetometer. e experimental setup is shown in Figure 22. e UAV fl ew a commanded trajec- tory in Irvine, California, USA, over a 155-second period during which 2 Orbcomm LEO satellites were avail- able (FM 108 and FM 116). Figure 23(a) depicts a skyplot of the satellite trajec-

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