## 4 Test Description and Equipment  
A data collection experiment was carried out in a vehicle in downtown Calgary, Canada on 22 July 2010 in the afternoon around 2:00 pm local time. Downtown Calgary is a typical urban scenario,  
Figure 3: Velocity/height constraints aiding scheme. characterized by skyscrapers and so it is a difficult environment for satellite navigation because of blocking and multipath problems. The total duration of the test is about 23 min; the speed of the vehicle varied from 0-50 km/h with frequent stops due to the traffic lights and the total distance travelled is about 10 km. The test equipment consists of a satellite receiver and a MEMS IMU (whose specifications are in Table 1) to perform the experiment and more accurate devices as reference. Specifically, the NovAtel Receiver ProPak V3--able to receive GPS and GLONASS satellite signals--and a Crista IMU from Cloud Cap Technology are used to test the different configurations. It is acknowledged that the use of a high quality receiver is inconsistent with the theme of a low-cost system. However, no low-cost GPS/GLONASS receiver was available for testing. Nevertheless, the differences obtained between using GPS-only and GPS and GLONASS together are expected to be largely receiver independent. The reference solution is obtained using the NovAtel SPAN (Synchronized Position Attitude Navigation), an integrated system consisting of the OEM4 NovAtel receiver and the HG1700 tactical grade IMU. The SPAN data are processed by NovAtel's Inertial Explorer software using phase and Doppler measurements in double difference mode. The baseline separation (relative to a base station located on the University of Calgary campus) varied between 6-7 km. The reference solution accuracy in these conditions is summarized in Table 3. All the equipment was placed on the roof of the car as showed in Figure 4 and the complete trajectory test is shown in Figure 5.  
To facilitate the data analysis, three segments of the trajectory, representing different operational scenarios, are considered and examined separately. The visibility and GDOP behavior is shown in Figure 6, where also the segments are highlighted. The GDOP parameter is a geometry factor, representing the amplification of the standard deviation of the measurement errors onto the solution [21]. \begin{table}
\begin{tabular}{c c c c} \hline
**Segment** & **GNSS Constellation** & **Solution Availability** & **Longest Solution Outage** \\ \hline \multirow{2}{*}{1} & GPS & 73\% & 60 s \\  & GPS/GLONASS & 81\% & 30 s \\  & GPS & 53\% & 60 s \\ \multirow{2}{*}{2} & GPS/GLONASS & 55\% & 60 s \\  & GPS & 81\% & 10 s \\ \multirow{2}{*}{3} & GPS/GLONASS & 86\% & 8 s \\ \hline \end{tabular}
\end{table} 
Table 4: GNSS availability and outage duration. Figure 5: Test trajectory (from Google Earth). Figure 6: Visibility and GDOP during the test. The main features of the GNSS coverage during all segments are summarized in Table 4, in terms of solution availability and maximum outage duration. This clearly shows the benefits of including GLONASS observations in this scenario. The segment 1 started in a parking lot where the satellite visibility was good and the operational conditions can be considered semi-open sky (4-10 visible GPS satellites). The second part of the segment 1 was in a demanding urban canyon with poor satellite coverage (0-6 available GPS satellites). The satellite visibility in the GPS-only and GPS/GLONASS cases is shown in Figure 7. In the GPS-only case, frequent partial and total outages are evident, particularly towards the east end of the long east/west part of the trajectory and along the north/south part of the trajectory (located near the center of downtown Calgary).