Hình Cấu trúc của máy dò đa tầng cho lặp đi lặp lại hủy bỏ sự can thiệp song song mềm ước tính trung bình = u = rv = u / MV, v. Trừ họ từ ru dẫn đến dự toán được cải thiện (0) au sau khi phiên đầu tiên. Việc huỷ bỏ giao thoa đồng thời áp dụng cho tất cả (1) ~ (μ) người sử dụng | MULTIUSER DETECTION IN CDMA SYSTEMS 241 Figure Structure of multistage detector for iterative parallel interference cancellation soft estimates ãV u rv u Mv v. Subtracting them from ru leads to an improved estimate aW after the first iteration. The interference cancellation is simultaneously applied to all users and repeated with updated estimates ãỈ 1 in subsequent iterations. In the -th iteration the u-th symbol becomes ã p M-u u-1 Nu ru - Muvãr1 - Ẽ MuVtf---1 v 1 v u 1 The simultaneous application of for all symbols ãu 1 u Nu is also called Jacobi algorithm and known as linear parallel interference cancellation PIC . An implementation leads directly to a multistage detector depicted in Figure Honig and Tsatsanis 2000 Moshavi 1996 . Several identical modules highlighted by the gray shaded areas are serially concatenated. Each module represents one iteration step so that we need m stages for m iterations. The choice of the matrix M determines the kind of detector that is approximated. For M R we approximate the decorrelator and the coefficients Mu v Ruv used in equal the elements of the correlation matrix. The MMSE filter is approximated for M R ơ A INu. Hence the diagonal elements of M have to be replaced with Mu u Ru u N0 Es. Convergence Behavior of Decorrelator Approximation The convergence properties of this iterative algorithm depend on the eigenvalue distribution of M. Therefore is described using vector notations. The matrix A diag diag R is diagonal and contains the diagonal elements of the correlation matrix R. The PIC approximating the decorrelator delivers aZ0F A 1-r a 1 A-1 r ÍR Aial0 A-1 2 iTv a-1 2ír a a-1 21 A-1 2r aZF A r - R - A aZF A INu - A R - A A A r 242 MULTIUSER DETECTION IN CDMA SYSTEMS u A-1 r _ Fo _ Ala 1 aZF A _r - R - A aZFJ A-1 2 INu - A-1 2 R - A A-1 2 A-1 2 R - A A-1 2 2 A m am A-1 2 2 A-1 2 A - R A-1 2f A-1 2r. 1 2r 1 0 The output after the m-th iteration in represents the m-th order Taylor .
