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In PosApp (SimGEN) what is the g-sensitivity feature for and how do I use it?


This article relates to users of PosApp in its SimGEN mode of operation. The g-sensitivity option can be found within the [Vehicle-->Options] part of the scenario tree.

As the name suggests, g-sensitivity allows the user to model the sensitivity of the receiver clock (crystal) frequency as a function of applied acceleration. The term "piezo-electric effect" might also be used when describing the behaviour of the receiver's clock frequency under these circumstances. g-sensitivity equates to a varying receiver clock error rate as the direction and magnitude of the applied acceleration changes. In PosApp this effect is applied as a pseudorange rate offset and an accumulated pseudorange offset. These offsets are accurately propagated as a function of the vehicle acceleration components (including all gravity and vehicle manoeuvre effects) and are the same for all satellites.  Note that this offset is not included in the logged pseudorange error,  but is included in the logged pseudorange and pseudorange rate data.

As an example, for a static vehicle if we enter a g-sensitivity value of 1.0e-8 s/s/g for each body axis (which is half the allowed range and probably an order higher than is seen in practice) this gives a pseudorange offset rate of 2.98m/s due to gravitational acceleration. At the receiver this will just appear as a linear clock drift term. However, if the vehicle motion is highly dynamic with large and sudden changes in acceleration then this will introduce a more random element into the apparent clock drift.  Note that PosApp models this effect as a fixed rate offset over the selected simulation iteration rate interval, so using an interval of 10ms instead of 100ms might be preferable to reduce the magnitude of step changes when considering high vehicle dynamics.

g-sensitivity is available for general use and isn’t specific to any particular receiver type. The appropriate section of the SimGEN user manual, DGP00686AAA, provides further details of the underlying equation used by PosApp.

Product : SimGEN,PosApp,Pseudorange,Vehicle,Receiver