SSOR preconditioned CG method for the linear interference cancellation of asynchronous CDMA systems

An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires computational complexity of order K³ when there K is the number of users. To alleviate the computational complexity, iterative decorrelating and LMMSE detectors are proposed for solving a set of linear equations corresponding to linear interference cancellation structures. Iterative conjugate gradient (CG) method has been used for the linear interference cancellation detectors. Its main advantages are to reduce the order of computation complexity and their suitability to highly parallel implementations. In this paper, the symmetric successive overrelaxation (SSOR) preconditioning scheme is applied to the CG method. The performance of the detectors is investigated and it is found that the SSOR preconditioned CG method can provide significantly faster convergence than CG method.