Blind period selection for cyclic adaptive multiuser detection in multirate multimedia CDMA systems

The problem of blind adaptive multiuser detection in multirate CDMA systems is considered. Since symbol detection in multirate CDMA systems requires periodically time-varying processing of the observables, classical LMS and RLS adaptive algorithms, which assume that the solution to be tracked is time-invariant or slowly time-varying, are not suited for blind adaptive multiuser detection in a multirate system. To overcome this limitation, cyclic adaptive algorithms have recently been developed. However, these algorithms are not truly blind, since they require knowledge of the data-rates of the interfering signals, so as to compute the period at which the cyclic algorithms should be run. This paper presents an adaptive procedure for the automatic selection of the algorithm periodicity, which is based on a minimum mean-output-energy criterion, and that obviates the need of such prior knowledge. Simulation results confirm that the proposed algorithm is effective and incurs a limited loss with respect to the case in which the data-rates of the interferers are assumed known.