In overloaded CDMA systems the high correlation among users’ signatures determines an overall performace that can be quite poor even for the optimal ML receiver. The geometric properties of signatures affect users’ separability, a condition that is necessary for achieving asymptotic efficiency. In this paper we establish gaussian separability conditions and propose an algorithm for the design of users’ gain in a way that guarantees users’ separability. Simulations show that the overall system performace can benefit of properly designed gain distribution as low-complexity iterative receivers can get near-optimal performances.