Optimal multistage interference cancellation for CDMA systems using the nonlinear MMSE criterion

This paper proposes an optimal multistage interference cancellation scheme for a multiuser DS/CDMA system with linear or nonlinear modulation. The proposed canceler is optimal in terms of minimizing the energy of the difference between true and reconstructed interference due to each user. Solutions for the special cases of BPSK and M-ary orthogonal modulation are derived using the general solution and efficient architectures are proposed for implementation. A novel blind channel estimation strategy based on an adaptive filtering approach that yields unbiased channel estimates and low estimation variance is also proposed. Simulation results indicate that the proposed scheme achieves substantial capacity gains with very little additional computational complexity compared to the conventional multistage canceler.