Hello, here's some advice:

What you need is called a 'matched filter'. This one is the
*optimum* filter, and you'll have to design it depending on
what signal was sent to you. Not a easy topic to explain here,
sorry.

Hint: place your question in the newsgroup comp.dsp,
meanwhile use a search engine with some of these keywords:
matched filter signal buried noise recover

For those of us interested, the matched filter come from the
development of the RADAR in the WW.

Regards,
Enrique.