Monthly Archives: April 2009

Fixed Subchip error

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Sources of Position Error

Incorrect pseudoranges can be a source of caluclation errors.
A type 2 PLL should be used.
Integrations/correlations inside the PLL should be done over 10-20ms.
This integration time will be dependent upon the maximum amount of gforce your application will experience.
For a stationary receiver integrations needed to be done faster than 1 second.
For an object traveling at 1 [...]

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Adjusting the sampling frequency

Because the pseudoranges are calculated from the sampling frequency of the device, any error in this number could result in the numbers being scaled incorrectly.
At a sampling rate of 16Mhz every Hz away from this is about .16 meters of error for a satellite.  When sampling at lower frequencies the effect is more dramatic.
I made [...]

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Altitude fluctuaions

I collected a couple of data points to monitor how the altitude changes according to the pseudorange calculations.
If I take the average of the altitude I get 300 meters which is correct.
The pseudoranges do not appear to have a high degree of noise in them, so I am thinking about averaging the last 10 positions [...]

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First working prototype.

I have completed the first prototype.
It is using gpstk for handling the subframes, and position calculation.
Now moving on to collecting more data sets.
Looks like the initial error is within 10-60 meters.
Ill try to clean up the prototype and post the binary.
Realtime Software GPS receiver on windows.

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Locating Preamble and Decoding data

Today I figured out why half of my data is being decoded correctly and the other half is not.
Turns out that the D30 bit of the previous word causes bits 1-24 of the next word to be inverted.
These bits need to be reinverted before they can be used.
Steps to locate and confirm the preamble are [...]

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