Research And Simulation Of OFDM Based On LDPC

OFDM technology with the high bandwidth efficiency is used to overcome the effect of multi-path fading. Encoding and decoding ways of LDPG with perfect performance of error correction, and applications in OFDM communication systems are studied in this paper. Two kinds of models of LDPC-COFDM communication systems are put forward. The emphases are: (1) research and simulation of OFDM system and key technologies. The characteristics of OFDM system are analyzed. Adaptive technologies and channel estimation and compensation technologies are adopted to simulate the physical layer of HiperLAN/2 and IEEE802.11a with Simulink based on time-flow, and to simulate DVB-T system with designing M file based on data-flow. Both ways give desirable results. (2) Constructing, encoding and decoding of LDPC. We analyze the characteristics of sparse check matrix and divide the construction ways of LDPC codes into three categories: random constructions, systemic constructions and sparse sequence constructions. Their advantage and disadvantage are discussed separately, and simulation is performed. By comparison, the results show that the construction ways of sparse sequence is more excellent and applicable than other ways. In encoding, we replace Gaussion-elimination ways with quasi-down-triangle matrix encoding ways not only to keep the sparseness but also to achieve the goal of encoding. In decoding, BP algorithm is good choice. According to the feature of OFDM system, we prove the feasibility of LDPC decoding algorithm for M-ary modulation. And then we come up with initial message algorithm. With the decoding algorithm, we simulate LDPC-BPSK, LDPC-QPSK and LDPC-8PSK systems separately on GF(2), GF(4) and GF(8), and acquire the desirable results. (3) A basic LDPC-COFDM and an improved LDPC-COFDM system are given. In multi-path Rayleigh fading channel, the simulation results of the basic LDPC-COFDM system with mediate SNR are not satisfying. However, the improved LDPC-COFDM system can acquire the desirable results with small SNR, which demonstrates the validity and dependability of the improved communication system in multi-path channel.