A Novel Approach to Improve the Iterative Detection Convergence of LDPC Coded CPM Modulated Signals

Continuous Phase Modulation (CPM) provides an attractive option for spectral efficient communication systems. Low-Density Parity-Check Code (LDPCC) combined with CPM has a potential to result in a spectrally efficient scheme that is also energy efficient in that it yields low error rates at low signal-to-noise ratios. In this paper we consider the concatenation of a LDPC encoder and a CPM modulator which can be decoded and demodulated iteratively. In order to decrease the positive feedback during iterative detection with short frame, an improved 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 effectively, but also reduce the average number of iteration as well as the iterative decoding delay.