[FOSS-GPS] High accuracy positioning with low cost GPS devices: a FOSS project

[John Morris]

> Do you have any ideas or suggestions on how to detect cycle slips 
> to improve your solution?

I'll give my opinion - but there are many others who have a better
background than me.

To detect and correct cycle slips, you have to already know your location
with a high degree of precision - say half a wavelength or better. Only then
can you detect and correct a cycle slip.

There are a number of ways refining your position, and some methods do it
implicitly.
(My descriptions aren't technically precise, but they illustrate the idea.)

  o RTK (real time kinematic) resolves the "integer ambiguities" to get a
very precise position.
    Slip detection requires a redundant satellite and is a matter of
    figuring out which satellite is the outlier.
  o Base station - the position doesn't change, so any unexpected Doppler
shift 
    can be attributed to cycle slips. Typically uses a Kalman filter and
takes some startup
    time for things to settle down.
  o Inertial sensors - use sensors (accelerometers, gyros) to dead reckon
the new position.
    Then it is very similar to the base station case, using Kalman filters
to detect inconsistencies.
  o Post-processing - gets a precise position before and after the slip by
averaging 
    pseudo-ranges. In practice, it could use a Kalman filter. There is a
significant delay
    between when the slip occurs and when the slip is detected, so this
method doesn't lend 
    itself to real time processing.

 - John