Inertial Navigation Testing

Posted in Applications

Different road designs, numerous types of intersections, and driving on the left or right-hand side are the tip of the iceberg when it comes to challenges faced by navigation system developers.

In addition, the cost of field testing in many countries and on different continents is large. So how do you accurately and consistently test your firmware or software? For many leading navigation suppliers and developers, the answer lies in record, replay, or simulation of GPS and Multi-GNSS signals.

SatNav testing

Why record and replay?

By recording scenarios in difficult signal reception conditions such as tunnels and underpasses, and by going on and off the scheduled route, the real life complexity of modern driving conditions can easily be captured in a way that is not possible with simulators.

These recorded scenarios can then be used time and time again to standardise your testing regime so that different versions of software and firmware can be verified to ensure consistent performance. You can even test different versions of your mapping database.

Testing dead reckoning (DR) capability

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 (DR) 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, we have developed a full navigation system testing solution comprising of a LabSat GNSS simulator, a Video VBOX data logger, a turntable, an inertial measurement and a wheel speed generation unit.

The turntable system uses global satellite constellation data to record live drive data combined with vehicle yaw rate and wheel speed information.

All of this data is replayed in perfect alignment so that the turntable will simulate the physical turning required to activate the DR in the navigation system under test. The wheel speed and satellite RF data will activate the navigation system and in combination with video provide a realistic replay of the driven route.

How does the LabSat Turntable system work?

The LabSat records live-sky GNSS data, and synchronised vehicle signals from CAN. The LabSat then replays this data,  containing GPS L1 signals and/or GLONASS L1 signals (along with any from Satellite Based Augmentation Signals (SBAS) WAAS/ EGNOS/ QZSS) back to the device under test - accurately reproducing the satellite and CAN signals from all of those which were present during the recording.

The turntable will rotate, simulating the yaw rate of the car in its original drive. This combination of physical rotation and GPS data will then activate the navigation unit’s gyro, and therefore its dead-reckoning system.

As it is based on a real recording the data will replicate the satellite signal loss experienced in city centres and tunnels and maintain the dead reckoning solution until the signals are regained, just like the live drive. This makes the replay repeatable time and again to save you significant testing costs.

Why use video recording?

LabSat turntable software has the ability to replay a Video VBOX video recording in synchronisation with the live recorded satellite data file. This will allow you to visually compare the position with the test performance. This is particularly useful in assessing the navigation system in and out of tunnels and in areas of poor satellite reception. All the replay data is managed by the LabSat software which has the flexibility to repeat the replay continuously to allow for accurate comparison and analysis.

The Video VBOX system can also create a custom scene in which a range of user defined data can be displayed on the video replay. This includes logos, headers, receiver data and information from the IMU. The picture within picture feature can also record the real time navigation screen data in a test vehicle, as well as the forward facing camera picture.

LabSat 3 Turntable solution

Testing around the globe

SatGen simulation software can easily create a route and output artificial satellite RF data files. By uploading NMEA or KML files or by using the Google Maps interface a complex route can be defined and recorded. When this simulated signal data is replayed the system generates the yaw rate and wheel speed data required to operate the turntable and the navigation unit being tested.

By removing the Satellite data feed GNSS signal loss can easily be replicated in the navigation system whilst the DR function remains active.

SatGen software with an imported KML file
SatGen software with an imported KML file