Fast CDMA multiuser detection by orthogonal projection onto an interference null space

This paper presents a method for asynchronous code-division multiple-access (CDMA) multiuser detection that has low computational complexity and that provides fast convergence. The proposed method efficiently finds an interference subspace from data samples and projects received signals onto its orthogonal complement to suppress multiple access interferences. Its performance has been analytically investigated in terms of the signal-to-interference-plus-noise ratio (SINR). The steady-state SINR is substantially the same as the optimum when the interferences are strong compared with noise. As to the transient response, the orthogonal-projection-based method converges quickly outperforming other methods such as the stochastic-gradient (SG) multistage Wiener filter (MSWF) and the affine projection method, which have similar computational complexity. Simulation results validate its effectiveness.