27 Oct 2017
High accuracy positioning for autonomous vehicles
Autonomous vehicles are now being developed by many different manufacturers new and established. For these, very accurate positioning is required to enable the car to be able to move on its own, knowing exactly where it is to a point within a lane, for example.
GPS has been available for many years as an accurate positioning system and now other GNSS systems are coming on line to enable multiple options to provide the overall positioning. GNSS has now become the recognised term to encompass any satellite navigation system.However, whatever system is used there are many basic errors that are present: basic orbit inaccuracies, satellite clock errors, ionospheric and tropospheric propagation errors and multipath propagation. These limit the accuracy that can be obtained such that it is not sufficiently accurate for autonomous vehicles.
For the higher levels of autonomous vehicles, very accurate positioning is required to enable the position of the vehicle to be located to within a lane, or with respect to the edge of the road. Sub-metre accuracy is required to provide the needed positioning for the automobile.
Many steps have been made to improve the accuracy of GNSS systems. By adding additional frequencies to provide signals using multiple frequencies has significantly reduced propagation errors, but other errors need a correction service to add local correction data.
To be able to send this data to any vehicles multiple schemes must be used to ensure that full coverage is achieved. Both (Inmarsat) satellite and cellular communication is used. A independent company called Sapcorda has been set up by ublox, Bosch, Geo++ and Mitsubishi Electric to provide the correction data. The company was launched in August 2017 and test services are soon to start.
Using services like these, autonomous vehicles are steadily moving towards a reality and fully autonomous vehicles are not just on the horizon, but starting to become more of a reality in the not too distant future.
By Ian Poole
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