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

Abstract

SummaryIn 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 GaussSeidel 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.

A reduced complexity chip-level SOR-SIC multiuser detector for long-code CDMA systems

“…For both cases (a) and (b), it is easy to see the significant gap in computational complexity between the three detectors. CL-SOR-SIC detector [7] proposed RC-CL-SOR-SIC detector SL-SOR-SIC detector [3] CL-SOR-SIC detector [7] proposed RC-CL-SOR-SIC detector…”

“…while the CL-SOR-SIC detector proposed in [7] requires 8KMN + 2KN flops and the SL-SOR-SIC detector proposed in [3] requires (2NK 2 + (2K+1)KM + (2N-1)K ). Lastly, the decorrelator detectors requires at least (lower bound) ( 3 2 2 11 3 K K K + + ) flops [9].…”

“…This enables its practical implementation in long-code CDMA systems where the cross-correlation matrix is changing every symbol. Simulation results indicate that a considerable complexity reduction is obtained by using this scheme (the complexity of the proposed structure is 50% less than that of the structure proposed in [7] and more than 50% less than that of the structure proposed in [3]). …”

“…Therefore, a chip-level linear SOR-SIC detector that uses directly the spreading codes and avoids the recomputation of the cross-correlation matrix is necessary. Recently, a chip-level linear SIC detector (we call it CL-SOR-SIC for brevity) that is equivalent to the SOR has been proposed in [7]. The structure has been proven to converge to the decorrelator detector using two different approaches.…”

“…In this work, a reduced-complexity chip-level linear SOR-SIC multi-user detection scheme is proposed. The latter (we call it RC-CL-SOR-SIC for brevity) makes use of the spreading codes directly; however, unlike the structure proposed in [7], the computations between the dispreading and spreading blocks are performed at symbol level, which considerably reduces the computational complexity. We show that the new scheme is in fact a realization of the SOR iterative method used to solve systems of linear equations.…”