The Problem
PPM is a distributor for NovAtel, a global supplier of world leading positioning technology across many disparate applications. Their combination of GNSS & INS offers a high-performance navigation solution in less than ideal environments.
Evaluating the performance of and fault finding for GNSS receivers like the NovAtel product line is often difficult and complex and for PPM this was no exception given that the NovAtel OEM 7700 is able to track multiple GNSS constellations simultaneously.
The company was looking for a standard test for all their GPS/GNSS related product lines where repeatability was a factor for regression and performance testing. Live testing was an issue for PPM as many factors are variable such as atmospheric conditions, satellite positions, road conditions and vehicular motion; this was a concern for the team as those factors can heavily influence the data obtained but are near impossible to accurately replicate during ongoing live tests.
The LabSat 3 Wideband was a natural choice for PPM as it can record the raw radio signals in the GNSS bands and replay them, providing repeatable yet consistent tests. The ability to record external data synchronised to the recorded RF in the scenario file also allows additional user data to be recorded alongside the GNSS signals. When replayed on the bench the external data is synchronised accurately with the GNSS signal.
Using the LabSat 3 Wideband to record the RS232 output of the SPAN IMU allows for an accurate replay of the original data into the system under test. The IMU RS232 output will replay alongside the GNSS data to provide a full reproduction of the outdoor test that is easily repeatable. The repeated performance of the device under test can be recorded separately for comparison and analysis.
By using real world signals and SPAN data recoded on the LabSat 3 Wideband, the engineering team at PPM were able to fully test the complete system data flow without the need to leave the office saving both time and expense. They also had an infinitely repeatable test procedure which they could use to test any device in the future with full confidence.
The Novatel OEM 7700 can track the following signals:
- GPS L1, L2c & L5
- GLONASS L1 & L2
- BeiDou B1, B2 & B3
- Galileo E1, E5 & E6
- QZSS
- IRNSS L5
LabSat 3 Wideband system can record and replay any signals in the upper and lower L band including:
- GPS L1, L2c & L5
- GLONASS L1 & L2
- BeiDou B1, B2 & B3
- Galileo E1, E5 & E6
- QZSS
- IRNSS L5 & S band
PPM engineers installed a LabSat 3 Wideband in a test vehicle together with a Novatel OEM 7 SPAN system to record the GNSS RF Signal input and the RS232 output from the SPAN IMU.
They mounted the GNSS antenna directly above the IMU with the OEM 7 alongside. The compact size of the LabSat and its data connections meant it could be conveniently mounted on the table of the vehicle. To ensure the OEM 7 & IMU initialization were recorded correctly, the OEM 7 was allowed five minutes to lock onto live GNSS signals. The SPAN IMU was then powered so that the handshaking and initialization were recorded correctly. The vehicle was moved off and conducted the live test along a route selected by the team.
In this test configuration the antenna being used was connected directly to a GNSS splitter, the splitter was then connected to the Novatel OEM 7 and the LabSat 3 Wideband. Using the splitter ensured the LabSat recording exactly replicated the original signal received by the OEM 7. The IMU output was also split using a Serial Y Cable splitter allowing data to pass to the OEM 7 and LabSat while remaining in sync with the GNSS data.
Once testing was completed the combined GNSS and IMU RS232 data was available for replay into any device under test. As the IMU initialisation sequence was captured during recording, the LabSat 3 Wideband can be connected to the OEM 7 directly to provide the GNSS and RS232 input without the need for an IMU to be connected.
The PPM team were also interested in LabSat 3 Wideband’s ability to record any differential data including RTCM for RTK positioning. The data recorded will include any anomalies including satellite outages caused by tunnels and buildings.
LabSat 3 Wideband replayed the recorded GNSS and IMU data to the OEM 7 during bench testing, with the OEM 7 successfully obtaining satellite lock and IMU initialisation.
Multiple replays were performed using LabSat 3 Wideband to confirm the viability of this test method. During this process it was determined that the OEM 7 can consistently initialise the IMU from the LabSat RS232 output with no IMU physically connected to the device.
Over the multiple replays performed the GNSS position was also analysed and proved to be repeatable, with the logged position trace giving a visual representation of the minimal variation between each replay.
Based on the use of a LabSat 3 Wideband during testing PPM were able to reduce the volume of equipment needed to test and dramatically reduce manpower and time taken in all areas of testing such as product compatibility testing.
Other customers
u-blox
Qualcomm
Intel
