Abstract
We introduce a chip-level linear group-wise successive interference cancellation (GSIC) multiuser structure that is asymptotically equivalent to block successive over-relaxation (BSOR) iteration, which is known to outperform the conventional block Gauss-Seidel iteration by an order of magnitude in terms of convergence speed. The main advantage of the proposed scheme is that it uses directly the spreading codes instead of the cross-correlation matrix and thus does not require the calculation of the cross-correlation matrix (requires floating point operations (flops), where is the processing gain and is the number of users) which reduces significantly the overall computational complexity. Thus it is suitable for long-code CDMA systems such as IS-95 and UMTS where the cross-correlation matrix is changing every symbol. We study the convergence behavior of the proposed scheme using two approaches and prove that it converges to the decorrelator detector if the over-relaxation factor is in the interval ]0, 2[. Simulation results are in excellent agreement with theory.
Highlights
Actual cellular systems such as IS-95 and UMTS are longcode CDMA systems
The proposed linear weighted group-wise successive interference cancellation (GSIC) detector which we call for brevity the chip-level linear block successive over-relaxation (BSOR)-GSIC detector consists of group interference cancellation units (GICU) arranged in a multistage structure of M stages as illustrated in GICU, is first despreaded, multiplied by a transformation matrix Rg−,1g and by a weighting factor μ to estimate the vector of the partial decision variables ym,g of users of the gth group at the mth stage that is ym,g = μRg−,1g STg em,g
This approach allows the identification of the proposed scheme as the BSOR iterative method, which facilitates the determination of the condition of convergence
Summary
Actual cellular systems such as IS-95 and UMTS are longcode CDMA systems. The spreading codes used in the uplink channels are long codes which span thousands of symbols. We prove that the proposed scheme in [6] is equivalent to the block Gauss-Seidel iterative method if the group-detection scheme is the decorrelator detector. The first contribution consists of identifying the structure proposed in [6] as a block Gauss-Seidel iterative method if the group detection scheme is the decorrelator detector. This is very important because it enables the use of the rich theory of iterative methods to study the convergence behavior of the scheme in [6]. Nonlinear group detection can be found in a work such as the one reported in [8]
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