A local converse theorem for U(2,2)

Let F be a p-adic field and let E/F be a quadratic extension. In this paper, we prove the local converse theorem for generic representations of U-E/F(2, 2) if E/F is unramified or the residue characteristic of F is odd. Our method is purely local and analytic, and the same method also gives the local converse theorem for Sp(4) (F) and (Sp) over tilde (4) (F) if the residue characteristic of F is odd.