Practical iterative multiuser detection for turbo encoded signals in CDMA systems

A practical iterative multiuser detection technology for code division multiple access (CDMA) systems, particularly for Universal Mobile Telecommunications System (UMTS) frequency division duplex (FDD) mode with long spreading code, is presented. A number of papers about combination of turbo decoder and multistage interference cancellation have been published. However, some practical issues such as computational complexity, processing latency, size of memory and multiple users with different code block lengths and asynchronous transmission timing intervals (TTIs) have not been addressed. With these practical issues in mind, we design a new receiver that combines modified iterative turbo decoder and multi-stage parallel partial interference cancellation (PPIC) in such a way that both turbo decoder and PPIC mutually benefits from each other. In addition, the partial cancellation coefficients are adaptively determined based on mean value of soft decisions of turbo decoder to improve performance. Simulation results are presented to demonstrate efficiency of the receiver.