Study On Some Turbo Codes Problems Of WCDMA System

In this report, a thorough analysis and research on the special multiplexing and channel coding project of WCDMA system is presented firstly based on 3GPP physical layer protocol.Then, the principle and the iterative decoding algorithm of Turbo codes are introduced. A proper simulation model of Turbo codes is selected based on the characteristics of WCDMA wireless channel. The influence of different parameters on the performance of turbo codes is simulated. The parameters include iterative decoding algorithms, interleave length, the times of iterative decoding and channel models.To reduce the decoding delay and the average iterative times, a few stop-iterative-criterias used as a rule are compared and analyzed, and an improved Turbo-CRC-SDR stop-criteria is brought forward. The new criteria can adopt relevant stop-iterative-criteria according to different channel conditions. The simulation results show that the improved method can decrease the average iterative times evidently with fewer capability losses.In the end, a simulation processing experiment regarding channel coding, multiplexing, decoding and demultiplexing for downlink of WCDMA is implemented using MATLAB Simulink toolbox. The simulation channel models include additive white Caussian noise channel and multi-path Rayleigh fading channel. For different channels, an error rate graph which is related to the channel coding and multiplexing is obtained, and the validity of the improved method is verified.