question about filter design vhdl

Hi, I have to design a low pass filter in VHDL. How can one go about designing such a filter when the medium is event driven and time domain based?? How should one decide on the filter characteristics if we just know the symbol time rate. If I am using standard VHDL and not AMS is it possible for me to design such a filter which is used in the recovery loops of receiver? Most of the references on filter and digital communications refer to frequency domain analysis. How can I go around this problem? If the input is a pulse then a low pass filter is an integrate and dump. However if I have a sampled sine wave how could I design a low pass filter? Could you please reply and let me know? I would grealty appreciate your reply. Looking forward to your replies, Thanks Viswanath PS: I would be needing a filter after the mixing of two sine waves to filter out the higher frequency components