Hi Dima,
What you in DSP is called interpolation. If you have accessed to
IEEE filter, try to locate a paper call Farrow structure, it is an
efficient implementation for the interpolation (using first order,
second order, or higher)
As for the "lambda" term, I guess you have already figured out. But
you may also consider to use a huge counter (the larger the bits, the
higher the resolution) to count the relative position. (you can use the
remainder as the lambda)
Your project really interests me, I am quite familiar with these
interpolation tricks using digital filters interpolation. Let me know a
bit more detail and maybe I can help.
Carson