Asymptotic analysis of widely linear MMSE multiuser detection-complex vs real modulation

We give the asymptotic signal-to-interference ratio for the so-called widely linear minimum mean-squared error multiuser receiver for transmission of multiple users to a common receiver with DS-CDMA. Observing that widely linear multiuser detection virtually doubles the spreading factor, we show that transmission with real-valued channel symbols can lead to a higher spectral efficiency than with complex-valued channel symbols when each user employs its own complex-valued random spreading sequence.