Asymptotic multiuser efficiency in overloaded CDMA

We consider overloaded CDMA systems where detection is performed with linear receivers and we find that in such systems it is possible to detect only a fraction of all users simultaneously, at most the spreading factor, with a probability of error that vanishes to zero as the channel noise goes to zero. To overcome this problem nonlinear detectors are required and we propose a simple iterative detector (that we call conditional conventional detector), based on filters matched to users´ signatures. Simulations show that indeed the proposed detector can be asymptotically efficient for all users at the same time.