The Research Of OCDM Technology For Optical Wireless Communication System

Nowadays,with the rapid development of information technology and the exponentially increasing demand of communication,the disadvantages of traditional radio frequency communication is gradually appearing.To solve those problems,the technology of optical wireless communication emerges as the time requires.To meet the requirements of the big data volume and the high communication rate,and to relief the insufficient spectrum resources,the research on advanced modulation technologies has been widely discussed.In recent years,the orthogonal chirp division multiplexing(OCDM)technology,which is proposed by foreign scholars inspired by orthogonal frequency division multiplexing(OFDM),has become a competitive signal modulation scheme in advantages of its excellent anti-interference performance.In this thesis,the transmission model of the optical wireless communication system which combines the optical wireless communication and the orthogonal chirp division multiplexing technology is studied.At the same time,the paper explores the channel equalization scheme of the system.This paper is specified in the following aspects.Firstly,the basic theory of orthogonal chirp division multiplexing technology and the OCDM system is introduced.Based on the concept of Fresnel transform and chirp spread spectrum technology,the principle of OCDM is analyzed.In the following,digital implementation of OCDM is deduced by using the discrete Fresnel transform.Finally,the traditional OCDM system model is given and its performance is compared with OFDM system.Meanwhile,the characterics of the underwater channel is studied from the aspects of the absorb and scatter of the sea water to explore the attenuation effect of seawater on light,and provide a theoretical basis for the experimental design of underwater wireless optical communication.Secondly,an IM/DD-OCDM system for optical wireless communication is studied.Combined with the previous research and the characteristics of the OWC system,the IM/DD-OCDM system which can be applied in the OWC scene is proposed.The realization of each part of the system is introduced in detail.The performance of the system is studied by simulation,and the results show that the system can transmit data normally under the channel when the SNR is greater than 12 d B.Thirdly,the channel equalization technology of optical wireless communication system is studied.The common methods of channel equalization are introduced.Three channel equalization schemes is given for the system proposed in this paper.By using OptiSystem,an optical communication simulation software,the performance of the system is verified under different wireless optical channel conditions,and the equalization effect of the proposed channel equalization scheme is compared.The simulation results show that the three equalization schemes can be applied to the proposed IM/DD-OCDM system and achieve a certain equalization effect.Finally,the IM/DD-OCDM system is verified by experiment.Combined with M-QAM modulation,experiments are set up in the laboratory to carry out underwater wireless optical communication research.The experiment proves that the OCDM technology studied in this thesis is feasible in underwater wireless optical communication,and can be combined with higher order modulation mode to improve the system communication rate when the system bandwidth is certain.