Hierarchical Decoupling Principle of a MIMO-CDMA Channel in Asymptotic Limits

We analyze an uplink of a fast flat fading MIMO-CDMA channel in the case where the data symbol vector for each user follows an arbitrary distribution. The maximum spectral efficiency of the channel with CSI at the receiver is evaluated analytically with the replica method. The main result is that the hierarchical decoupling principle holds in the MIMO-CDMA channel, i.e., the MIMO-CDMA channel is decoupled into a bank of single-user MIMO channels in the many-user limit, and each single-user MIMO channel is further decoupled into a bank of scalar Gaussian channels in the many-antenna limit for a fading model with a limited number of scatterers.