Spreading Codes Enabling Warp Converging Wiener Filters for Multiuser Detection in CDMA Systems
It has been shown in the authors' previous work that for signal modes with a specially structured data covariance matrix, a warp (stable and predictable early) convergence can be achieved using the Reduced-Rank Conjugate Gradient (RRCG) Wiener Filter (WF) for MUltiuser Detection (MUD) in Code Division Multiple Access (CDMA) communication systems. In this paper, they study various commonly used spreading codes that enable warp converging of the RRCG-WF. By analyzing the eigen-structure of the code set Grammian, they provide the exact number of convergence steps for different code sets. It turns out that this number varies from 1 to 4 based on different spreading sequences, implying greatly reduced computational complexity of the RRCG-WF for MUD in CDMA systems.