  We have considered the BCS-BEC crossover at T=0 in the framework of a lattice
fermion model (the extended Hubbard model). We have analyzed the case of
on-site hard core repulsion ($U=\infty$) and intersite attraction ($W<0$) in a
3D system with extended s-wave pairing symmetry. The mechanisms of
density-driven and attraction-strength-driven crossover have been analyzed. We
have obtained the ground state phase diagram. The analyzed quantities are:
chemical potential, order parameter, coherence length and fraction of condensed
particles.
