|Testing in the absence of GPS|
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To cover for losses in satellite visibility, which can occur in urban canyons, tunnels and under bridges, most OEM navigation systems have a dead reckoning capability that utilises vehicle wheel speed data and turn rate information. When it comes to testing these systems on the bench, if the dead reckoning signals are not present, the navigation systems will not function correctly. To overcome this, UK based electronics company Racelogic has introduced a full navigation system testing solution comprising of a LabSat GPS simulator, Video VBOX data logger, turntable, yaw rate sensor and wheel speed generation unit.
To record the data, the LabSat and Video VBOX are placed in the vehicle during a simple drive along the desired test route. The wheel speed data is recorded from the vehicle CAN bus, and the yaw rate sensor records the physical movement of the vehicle.
Back in the laboratory, the LabSat recreates the GPS data, the wheel speed generation unit outputs synchronised wheel speeds and the data from the yaw rate sensor drives the turntable on which the navigation system is placed. This unit then has all of the information it requires to operate as normal, under all conditions. As an added benefit, a fully synchronised video is displayed showing the progress of the vehicle along the route, allowing the user to see the exact conditions which were present during the recording of the data.
An alternative method to recording the data during a test drive is to generate an artificial scenario using the SatGen software package. The yaw rate and wheel speed data are then synthesised from the trajectory data in real time, driving the turntable and generating wheel speed data. This gives engineers the ability to simulate any journey, conducting tests from thousands of miles away at any time or date, and still be assured of the results.
For example, engineers based in Tokyo can create a test scenario based around Miami and check that the navigation system still works under these conditions. This trajectory data can be either be drawn on an interactive map, or created using existing NMEA data.