Coded Modulation With Low Density Parity Check Code

Coded modulation is an error control technique which is designed by integrating channel coding and modulation, in order to acquire multilevel gain and encoding gain at one time, as to improve the frequency efficiency and power efficiency of the wireless channel. Low-Density Parity-Check (LDPC) code has better decoding performance and higher decoding throughput comparing to Turbo code. Its excellent performance makes LDPC code become an optional channel code for different standards (such as IEEE802.16e, IEEE 802.11, IEEE 802.20, DVB-S2, CCSDS, et.al). In order to improve the transmission efficiency of the system, and to get the high encoding gain, we can consider integrating the LDPC code with high order modulation.Based on the understanding of the theory of LDPC code and its encoding and decoding algorithm, coded modulation system with LDPC code is researched. Through software programming, the system of Bit Interleaved Coded Modulation(BICM) integrating LDPC code and 16QAM modulation and the system of Multilevel Coding(MLC) integrating LDPC code and 64QAM modulation is designed base on the Gaussian channel. On the research of Unequal Error Protection (UEP), constellation partitioning scheme and designing of component codes is analyzed. Based on the research of high order soft modulation, an approximate demodulation to reduce the algorithm complexity is proposed. The simulation results show that the bit error performance of the approximate demodulation is close to the standard demodulation. In tht coded modulation system with LDPC code, Phase Noise in Channel may result in the circumrotation and the excursion of the received constellation, which result in the distortion of the received signal. Take measures of the method of demodulation, a kind of improved high order soft dmodulation is proposed, which changes the region of the hard decision to reduce the bad effect of phase noise. This improved dmodulation used in the system of BICM achieved good performance by simulation. The improved demodulation scheme of MLC is the main investigating derection.