Multiuser interference mitigation with multistage detectors: design and analysis for unequal powers

Asymptotic multistage detectors reach a good compromise between Performance and complexity for large size systems. However, design criteria and performance analysis are available only for additive Gaussian noise channels and equal received power users. We provide equations to precisely calculate the asymptotic weighting of multistage detectors for random CDMA satisfying the individual and joint LMMSE criteria in the projection subspace for scenarios with unequal powers. Additionally, a general expression of the SINR achievable at the filter output as system size grows large is derived. Such equation can be applied to any multistage detector. We specialize this result to both the individual and joint LMMSE multistage detector with asymptotic weighting. We show that the individual LMMSE detector outperforms the joint LMMSE detector in the case of unequal received powers while the detectors are equivalent in the case of equal received powers. Performance degradation of the asymptotic multistage detectors, when used infinite large systems, is negligible compared to the correspondent optimum detectors for finite systems.