Multistage detection in synchronous code-division multiple-access systems

Although the optimal detection of signals in a K-user CDMA synchronous system has been proved to be NP-hard, some suboptimal methods do exist to approximate the optimal one. The authors develop a new multistage detector using the transformation proposed by Carter (1984) to approach the optimal solution. The transformation modifies the diagonal elements of the hessian matrix of the quadratic function corresponding to the optimal receiver and brings the continuous minimum of the transformed function as closely to the optimal solution as possible. The convergence of the new multistage algorithms is studied. The computational complexity is essentially linear with the number of users except that a few computations of a quadratic function are needed. The numerical results for the detection of synchronous CDMA signals are shown to be very encouraging