Unable to reliably get location while indoors with TAT140


I am setting up a TAT140 tracker which is supposed to track valuable goods travelling inside trucks and while they are being transferred inside warehouses.

I can get GPS coordinates when outside without issues, however, the getgps command (with two spaces at the start) sometimes returns 0.000000 for both coordinates when indoors.

What can I do to improve the reliability of the tracker when indoors? I believe that the TAT140 could use GSM triangulation, is that correct and if so, how can I enable it?

Thanks for any pointers