| The wireless optical communications is the outcome that optical communications and wireless communications combine, which have advantages of great capacity, high velocity and low price. Its position in communication domain is gradually important.Low-density parity-check code (LDPC) is now a Cutting-edge and popular coding scheme. Combining with efficient BP decoding algorithm, LDPC code has the performance of closing to Shannon limit.In this thesis, it is generated that the fundamentals of channel coding and the development of channel coding theory, in particular LDPC coding theory. The structure of LDPC codes is described. Based on the calibration matrix, Tanner graph representation, degree distribution of LDPC code, the various parameters of irregular and regular codes are defined. The decoding of LDPC code is also studied, such as the probability of the domain BP decoding algorithm and log likelihood ratio domain BP decoding. In this thesis, channel codes and modulations are also compared. Through simulation, we can see that LDPC code has better error correction capability, and in the longer codes, lower code rate cases, LDPC codes performance more superior. A study of Digital Pulse Interval Modulation (DPIM) is introduced, and the Pulse Position Modulation (PPM), On Off Key (OOK) and DPIM three kinds of modulation are compared. Then PPM and DPIM modulations are emulated by Simulink of Matlab. In order to facilitate the realization of the hardware, the quasi-randomπ—rotation LDPC code is studied. We use Simulink emulation tool to analyze the performance of the wireless optical communication system in the atmospheric channel based on DPIM modulation. The result shows that as the use ofπ—rotation LDPC code, the system performance has improved.Therefore, it is found that Low-Density Parity-Check Code (LDPC) based on Digital Pulse Interval Modulation (DPIM) is a suitable choice for the optical wireless communications.At last, some functional modules in the system are introduced. |
PDF Full Text Request