It is some time ago, that I was fighting with that model and how
to estimate the 3 parameters (until recognizing that one may want
restrictions for them).
Essentially one uses the statistics of the underlying data to get
a reasonable starting guess. 
For an estimation then one can use the Optimization package.
The gradients involved are best coded as a floating point library,
which here is done through a DLL (it should work on all Windows OS),
code in C is included for that.
Meanwhile all can be done using 'Compiler:-compile' or the Watcom
compiler delivered with Maple.
I left that older sheet as it is - in Maple 9 (may be one should
brush it up for concurrent Maple versions, they are grumbling a bit
about the code) and hope it is of interest despite of that.

Maple sheet:
DLL + code:
as a pdf:


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