How can GPS accuracy be improved?

Question

satellite navigation

We ran into GPS accuracy issues on mobile, tried Android and iPhone 5. Both have GPS+Glonass chips. While driving, the location determination occurs in jumps and often we can find ourselves inside a building or on a neighboring street. During the stop, the position also starts jumping in different directions.
How can accuracy be improved in urban environments? An external module for a computer or mobile, bluetooth modules for a phone, detection algorithms.

Answer 1

The accuracy of a single measurement by one receiver cannot be increased above that declared for navigation systems (this is ~ 10 meters of error at best). You can either use additional data (for example, for cars - binding to the road), or use Kalman filtering and many measurements.

Answer 2

You can simply determine the motion vector and average the data under it, only when 2 or more points go in the direction of changing the vector.

Answer 3

those. no external antennas will improve the signal quality?

Answer 4

An external receiver with a sufficiently large antenna installed outside the car reduces the error, but nothing can be improved better than the theoretically possible limit, which is due to the magnitude of the uncertainty of the method for determining the coordinates. The theoretical limit for a "clear field" when the whole sky is visible and the weather is clear is about three meters. The more obstacles (urban development, forest), the worse this limit.
Using the Kalman filter allows you to smooth out the jumps, but the accuracy does not improve - when the direction changes, the track will "skid", just its shape on a straight line will look straighter.