Journal of Systems Engineering and Electronics ›› 2014, Vol. 25 ›› Issue (5): 728-734.doi: 10.1109/JSEE.2014.00083

• ELECTRONICS TECHNOLOGY • Previous Articles     Next Articles

Optimized LDPC differential-encoded 16QAM scheme for high-speed transmission systems

Zhanji Wu1,*, Xiang Gao1, and Zhiyu Xiao2   

  1. 1. School of Information and Communication Engineering, Beijing University of Posts and Telecommunications,
    Beijing 100876, China;
    2. Huawei Technology Limited Corporation, Chengdu 610041, China
  • Online:2014-10-23 Published:2010-01-03


The 16-ary quadrature amplitude modulation (16QAM) is a high spectral efficient scheme for high-speed transmission systems. To remove the phase ambiguity in the coherent detection system, differential-encoded 16QAM (DE-16QAM) is usually used, however, it will cause performance degradation about 3 dB as compared to the conventional 16QAM. To overcome the performance loss, a serial concatenated system with outer low density parity check (LDPC) codes and inner DE-16QAM is proposed. At the receiver, joint iterative differential demodulation and decoding (ID) is carried out to approach the maximum likelihood performance. Moreover, a genetic evolution algorithm based on the extrinsic information transfer chart is proposed to optimize the degree distribution of the outer LDPC codes. Both theoretical analyses and simulation results indicate that this algorithm not only compensates the performance loss, but also obtains a significant performance gain, which is up to 1 dB as compared to the conventional non-DE-16QAM.