Research On Multiuser Detection In CDMA Mobile Communication System

Multiple access interference (MAI) in CDMA systems refers to the interference between non-orthogonal user signals. If MAI sources are closer to receiver than signal sources, the stronger MAI will overwhelm objective signal received by receiver. This phenomenon is called near-far effect. How to restrain MAI and near-far effect is an important research respect in CDMA systems. Multiuser detection exploits interference to restrain interference and possess strong capacity of diminishing near-far effect. The dissertation is focused on the research of parallel interference cancellation (PIC) and blind multiuser detection, the main contributions are listed below:1. Proposed a new minimum variance PIC (MV-PIC) detector for synchronous CDMA system, proposed the formula for the computation of the weighting factor which minimizes the variance of output variable and prove that it locates in the range of (0,1), functions of the expectation, variance and bit error rate (BER) are proposed as well. Computation with typical parameters shows that minimum variance weighting factor leads to the lowest BER. Simulations show that MV-PIC detector outperforms correlating detector, conventional PIC detector and partial PIC detector in synchronous channel.2. Proposed new correlating functions of asynchronous codes, which act as accurate mathematical model for asynchronous signal. Proposed a new minimum BER PIC (MBER-PIC) detector in asynchronous CDMA systems. Proposed the expectation, variance and BER function of MBER-PIC, proposed the formula for the computation of the weighting factor minimizing the BER, which is proven by simulations. Simulations show that MBER-PIC detector outperforms correlating detector, conventional PIC detector and partial PIC detector in asynchronous channel.