01 - Turntable Introduction
GNSS receivers rely on line of sight reception of the Global Navigation Satellite System (GNSS) signals to operate and any loss of reception due to signal obscuration in urban canyons and tunnels means that the receiver will not provide a constant navigation solution. To overcome this deficiency many systems use a dead reckoning capability (DR) to aid the navigation solution until suitable GNSS signal reception is restored.
For example most OEM vehicle navigation systems have a dead reckoning capability that utilises vehicle wheel speed data and rate of turn information. When testing these systems on the bench, if the dead reckoning gyros are not stimulated the navigation systems will not function correctly. To overcome this, we have developed a full navigation and DR system testing solution, LabSat Turntable System.
The system comprises a LabSat 3 GNSS simulator, Video VBOX data logger, Turntable and controller, yaw rate sensor and wheel speed recording, which can operate in three different modes:
- Record System – The mobile record operates in a vehicle to record real journey data. This data includes the LabSat 3 GNSS file, Video VBOX video recording together with yaw and wheel speed information. The system will record the real satellite signal performance from multiple constellations including signal loss through obscuration by buildings, trees, foliage, tunnels and motorway underpasses together with the signal multipath found in these poor signal reception areas.
The Video VBOX records a real-time video of the journey which can include picture in picture recording of the performance of the on-board navigation system screen. The Inertial Measurement Unit (IMU) records the vehicle yaw (rate of turn). Wheel speed data can be recorded from the CAN by the LabSat 3 or from an electronic speed pulse provided by the vehicle.
- Replay System – The replay system located in the testing facility can replay all the sensor data synchronised together to provide a realistic replay of the recorded journey. The turntable will replicate yaw (rate of turn) on the device under test (DUT) in sync with the GNSS signal replay, wheel speed information and recorded video. As further enhancement to the device testing is a video VBOX can be used to record the journey together with the performance of the display screen of the navigation system being tested. This video recording can be replayed alongside previous video recordings of test replays to provide a functional visual comparison.
- Simulation System – The simulation system allows for a route anywhere to be created in the SatGen v3 software. The artificially created GNSS RF file can be replayed by LabSat 3 with the turntable yaw rate and wheel speed information created by the system software to accurately replicate the journey created. Signal drop out by tunnels can be simply replicated by removing the antenna connection to the DUT.