An Improved Method for the Convergence of Iterative Detection in Turbo-CPM System

Based on the decomposed model of continuous phase modulation (CPM), CPM is divided into a continuous phase encoder (CPE) and a memoryless modulator (MM). Using the memorial and recursive character of CPE, combined with turbo code and random interleaver, the model of Turbo-CPM system is founded. In order to solve the problem of positive feedback during iteration with short frame, a method based on weighed extrinsic information exchange is proposed. Theoretic analysis and simulation results show that the proposed method can not only prevent the phenomena of positive feedback from taking place, reduce the error floor and improve the performance of BER under the condition of low SNR, but also reduce the average number of iteration and enhance the real-time. Furthermore, the method can avoid the conversion from probability to likelihood ratio and its inversion in the process of transferring extrinsic information, and reduce the complexity of decoding algorithm.