A new chip-level linear SOR-SIC multiuser detector for long-code systems

In this work, we introduce a new chip-level linear modified-SIC multi-user structure that is asymptotically equivalent to successive over-relaxation (SOR) iteration, which is known to outperform the conventional Gauss- Seidel iteration by an order of magnitude in terms of convergence speed. The main advantage of this scheme is that it uses directly the spreading codes and not the cross-correlation coefficients and thus reduces significantly the overall computational complexity. This is critical for the design of low-complexity multiuser detectors for longcode CDMA systems such as IS95 and UMTS.We use a matrix algebraic approach to show the equivalence of the proposed scheme to linear matrix filtering. This allows obtaining an analytical expression for both the bit-error rate (BER) and the asymptotic multiuser efficiency (AME). Moreover, we study the convergence behavior of the proposed scheme and prove that it converges if the relaxation factor is within the interval ]0, 2[. Simulation results are in excellent agreement with theory.