A matrix-algebraic approach to linear parallel interference cancellation in CDMA

In this paper, linear parallel interference cancellation (PIC) schemes are described and analyzed using matrix algebra. It is shown that the linear PI G, whether conventional or weighted, can be seen as a linear matrix filter applied directly to the chip-matched filtered received signal vector. An ex pression for the exact bit-error rate (BER) is obtained, and conditions on the eigenvalues of the code correlation matrix and the weighting factors to ensure convergence are derived. The close relationship between the linear multistage PIC and the steepest descent method (SDM) for minimizing the mea n squared error (MSE) is demonstrated, A modified weighted PIC structure th at resembles the SDM is suggested which approaches the minimum MSE (MMSE) d etector rather than the decorrelator, It is shown that for a K-user system, only K PIC stages are required for the equivalent matrix filter to be iden tical to the the MMSE filter. For fewer stages, techniques are devised for optimizing the choice of weights with respect to the MSE. One unique optima l choice of weights is found, which will lead to the minimum achievable MSE at the final stage. Simulation results show that a few stages are sufficie nt for near-MMSE performance.