An improved iterative decoding method for LDPC coded CPM systems in Rayleigh fading channel

The increasing number of users of mobile communication systems and the corresponding need for increased capacity show the importance of using a modulation scheme which is both power and bandwidth efficient. Continuous phase modulation (CPM) provides an attractive option for spectral efficient communication systems. Low-density parity-check (LDPC) codes 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, LDPC coded CPM which can be decoded and demodulated iteratively is considered for uplink of satellite communications. In order to reduce the positive feedback during iterative detection with short frame, an improved method based on weighed extrinsic information exchange is presented. Theoretic analysis and simulation results over Rayleigh fading channel show that the proposed method can not only achieve lower bit error rate (BER) and better convergence compared to the previous methods, but also offer very low error-floor and good BER performance in waterfall region. Meanwhile, the method can reduce the average number of iteration as well as the iterative decoding delay.