Study On Joint Detection In TD-SCDMA And Multi-User Detection In WCDMA And Performance Analysis

TD-SCDMA and WCDMA all are interfere-limited systems.There are multi-path interference, multi-user interference of intra-cell (Multiple Access Interference, MAI) and inter-cell interference, the MAI is the the major interference in CDMA system. Those destroy the orthogonality of each channel which reduces the utility of system's frequency-spectrum and performances.In conventional detections,the MAI only is seen as noise and the information of the other users are not used, which make the conventional detectors can not eliminate the MAI that will lead to deteriorate the system's performances.Thus, the WCDMA system uses Multi-User Detection (MUD) algorithms,as well as, the TD-SCDMA system introduce Joint Detection (JD) techniques in order to eliminate the MAI.This paper mainly studies the applications of JD in TD-SCDMA system and MUD in WCDMA system.Firstly, this paper introduces the basic principles of CDMA system and conventional detections.Through theoretical and simulation analysis, we know the conventional detectors can not eliminate the MAI, which will lead to seriously deteriorate the system's performances.Therefore, MUD and JD algorithms are leaded into systems.In this paper, MUD and JD algorithms are introduced, focusing on the analysis of the Parallel Interference Cancellation (PIC) and three kinds of JD algorithm——WMF, ZF-BLE and MMSE-BLE, also executing the performance simulations.As compared with conventional detectors, MUD and JD detectors,more effectively, suppress or eliminate the impact of so that they can better improve the system performances.Then,the concepts of the physical layer in WCDMA system are described, and the same time, according with the characteristics of the system, the WCDMA uplink simulation model and simulation diagrams are set up.By comparatively analyzing the not use of MUD and the use of MUD, in the WCDMA system that is a interfere-limited system, MUD algorithms can effectively suppress MAI, improving the performances of WCDMA system in a large degree and verifying the theoretical analysis results.Finally, introducing the basic formats of physical channel in TD-SCDMA,establishing the system's transmission model, and introducing and analyzing all aspects of model in detail.The main purpose of the JD techniques is accurately estimating the user's signal,the difficulty lies in the system matrix inversion, so to find the fast inversion algorithms is the main key to make better the JD algorithms.This paper, the process of system matrix inversion which uses the block FFT (Fast Fourier change) algorithm is derived in detail.Then, through simulating the ZF-BLE algorithm based block FFT, testing and verifying the algorithm's performances.Compared with ZF-BLE, the improved fast algorithm has a better BER performance and a higher operational efficiency, the improved fast algorithm reduces the computing magnitude, the storage multiply falls down than traditional algorithms,and better improving the system performances.