Asymptotic reduced-rank MMSE in asynchronous MC-DS-CDMA systems

We consider the design of a reduced-rank minimum mean-squared error (MMSE) receiver for asynchronous multicarrier-direct sequence-code division multiple access (MC-DS-CDMA) systems with random spreading. We focus on the asymptotic MMSE filter designs in the large system regime, i.e., both the spreading gain and the number of users approach infinity while their ratio is a finite constant and the number of subcarriers is finite. Explicit expressions for the asymptotic weights of the MMSE receiver are derived for the case where the spreading sequences are identical over different subcarriers for each user. Simulation results validate our analysis.