modelling and simulation of digital system

HI All,

   I want to model and simulate a digital system:

I/P is 2 volt pk to pk analog signal which will be digitized with 16 bit ADC (2's complement). this digitized signal has to mulitplied with ( digital Sine and cosine waves). The o/p has to filtered with a fix point FIR filter then sqaured and added.

I want to study effects of truncation at different stages.

I am attaching a basic model.

Please guide me.