Blind estimation of array responses for an asynchronous multiuser system

A prime task in a space-division-multiple-access (SDMA) system is to estimate the array response to each mobile unit, so that multiple co-channel signals can be separated using spatial diversity. Talwar et al. (1994) introduced a data-efficient blind estimation approach by exploiting the finite-alphabet property of a digital signal. However, the algorithm requires that the information bits from all users be perfectly synchronized. In this paper, we establish a practical model for an asynchronous multiuser system. Based on this model, we develop a novel estimation scheme which first synchronizes the multiuser system and then determines the array responses by integrating the techniques. RF field experiments show that the new approach can reliably estimate the array responses and separate multiple sources in some typical scenarios.