The Research Of Bit-interleaved Coded Modulation

ABSTRACT:Bit-interleaved coded modulation (BICM) is a typical code modulation techniques. It has simple structure and excellent performance intending to increase the diversity of coding. Against the shortcomings of TCM like poor flexibility and poor performance in fading channels, BICM design the encoder and modulator separately with ideally interleaving. So it can have a good robustness and a high degree of flexibility in fading channels. Since its invention in late1990s, BICM has been always being a focus in the research of CM and also adopted by various kinds of practical wireless communication systems, even will have a large-scale applications in the field of optical communications in the future. However, it still has some new technical difficulties:the known optimal constellation-mapping can not meet the high spectrum efficiency;irregular and non-optimal multi dimensional constellation-mapping don’t be given. The application of BICM based on the advanced codec technology (LDPC、Turbo) in optical communication has a growing concern, its research has great theoretical and practical significance.In this paper, we study and optimize the known multi dimensional constellation mapping for different channel types. Also, we analyze the result in the view of channel capacity. We further study some problems of LDPC-BICM system in optical communication. The following is the main content of the work:1. Firstly, we review the basic theoretical framework of BICM. Starting from the design of optimal symbol, we study and write binary switching algorithm (BSA). For AWGN and Rayleigh channel, we optimize the known multi dimensional constellation mapping with corresponding cost function based on the distance spectrum. Then we gives optimal results and the corresponding value of the cost function.2. Further, considering the two cases(ideal priori information and no a priori information), we simulate the capacity of BICM in AWGN and Rayleigh channel. We intend to get better system performance by contrast with MQAM constellation mapping capacity. Also, we analyze the impact on the optimization results of EsNo under the same dimension in AWGN channels.3. In the end of the paper, we study the performance of LDPC-BICM system in optical communication in view of residual dispersion and nonlinear phase noise. We Create different fiber channel models and simplify the corresponding formula. Then, we simulate the performance of LDPC-BICM system in optical communication by matlab-CML and analyze the tolerance for residual dispersion and nonlinear phase noise. In the simulation, we use the standard DVB-S2-LDPC code(code length-16200、 Rate-1/4)、Soft-output demodulation algorithm (Max-Log-MAP) and16QAM-Gray mapping.