Two-stage CMA blind multiuser detection for DS-CDMA systems in multipath fading

We consider the problem of mitigating intersymbol interference (ISI) due to multipath fading as well as multiple-access interference (MAI) in direct sequence code-division multiple-access (DS-CDMA) systems. The proposed multiuser receiver is based on the constant-modulus algorithm (CMA), which is known to provide satisfactory performance in a blind setting. In order to overcome the CMA interference capture problem typical of a multiuser scenario, we propose to adopt a two-stage receiver: in the first stage, partial MAI suppression is achieved by exploiting the desired user signature structure properties; in the second stage, based on CMA, the residual MAI and the ISI are removed, and the desired symbols are reliably recovered. Computer simulations show that, in a severe multipath environment, the proposed blind approach achieves a significant performance gain in comparison with existing blind methods.