The highest resolution GPS receivers have two changes:
1. Base stations at known locations broadcast corrections for factors like the effects of the ionosphere and troposphere, and inaccurate satellite ephemerides. If you have multiple base stations, you can interpolate between them (Trimble VRS Now [1] does this, for example)
2. Precise measurements by combining code phase (~300m wavelength) and carrier phase on two frequencies (~20cm wavelength), plus the beat frequency of the two frequencies (~80cm)
With these combined, and good visibility of the sky, centimetre-level accuracy is possible.
Autonomous vehicles will often combine this with inertial measurement [2] which offers a faster data rate, and works in tunnels.
Many people also expect autonomous vehicles to also track lane markings, in combination with a detailed map to say whether lane markings are accurate.
1. Base stations at known locations broadcast corrections for factors like the effects of the ionosphere and troposphere, and inaccurate satellite ephemerides. If you have multiple base stations, you can interpolate between them (Trimble VRS Now [1] does this, for example)
2. Precise measurements by combining code phase (~300m wavelength) and carrier phase on two frequencies (~20cm wavelength), plus the beat frequency of the two frequencies (~80cm)
With these combined, and good visibility of the sky, centimetre-level accuracy is possible.
Autonomous vehicles will often combine this with inertial measurement [2] which offers a faster data rate, and works in tunnels.
Many people also expect autonomous vehicles to also track lane markings, in combination with a detailed map to say whether lane markings are accurate.
[1] http://www.trimble.com/positioning-services/vrs-now [2] http://www.oxts.com/products/rt3000/