Ds Cdma Communication System, Multi-user Detection Techniques

In DS-CDMA communication systems, Multiple Access Interference (MAI) is the main cause to impact on the systems performance among so many different kinds of interference. The power of Multiple Access Interference (MAI) directly confines the capacity of DS-CDMA system.As the mainstream of MAI suppression technologies, multi-user detection (MUD) performs a significant role to improve the Bit Error Rate (BER) performance and to increase the capacity of systems. The main kinds of multi-user detection (MUD) technology are summarized since the theory of MUD has been developed in this paper. MUD receivers are divided into two kinds: Linear MUD and Interference Subtractive MUD. The principle of each MUD iscomment as long as its-strongpoint and shortcoming.A kind of MUD based on transversal equalizer is recommended, and the performance analysis of DS-CDMA systems based on that MUD has been done under synchronous channels. Then the expression of output signal is deduced. Also,the relations among SINR of output signal ,SNR and Correlation Matrix of Spread Code The least mean square error (LMS ) adaptive algorithm is applied to the MUD. According to the LMS criterion, steps for calculation implement is proposed., and simulations on convergency and BER properties blind algorithm has been done. In addition, as a introduction of blind algorithm,Subspace Decomposition, Minimum Output Energy(MOE). and Constant Modulus Algorithm(CMA) is refered.Results of computer simulations prove that the MUD has higher SINR value, effective MAI cancellation, better Near -Far resistance capability than Decorrelating MUD. So it's feasible and reasonable. Simulation results also show that the LMS algorithm can exactly converge to stationary value, works well on BER properties and adaptively detects the users' signals.