Research On Performance Of Indoor Visible Light Communication System Based On OCDMA

With the universal popularization of multimedia services and mobile internet devices,the limited wireless electromagnetic spectrum occupied by traditional radio frequency wireless communication is not able to meet the requirements of rapidly increasing data-rate and quality-of-service any more.In order to that serious problem,more and more researchers devote themself to develop visible light communication technologies.Whit the increase of the number of simultaneous users,solving the problem of multiple access has become one of the promblems that need to overcome in optical wireless communication.Compared with traditional multiple access technologies in optical wireless communication,optical code division multiplex access(OCDMA)technology which is of high anti-interference,flexible accessing,high channel utilization and so on,is widely used in the theoretical research of wireless optical communication.The OCDMA has been studied for more than 40 years,but only a smattering of researchers considered for the effect of multipath dispersion on communication system performance with line-of-sight transmission channel.Therefore,this paper mainly studies the influence of indoor visible channel in OCDMA system's BER performance.In this thesis,research significance and research progress of VLC and OCDMA technology are included firstly.And then,we present the architecture of indoor VLC system and indoor visible light channel model which have been analyzed and simulated in detail.The novel construction algorithm of optical orthogonal code(OOC)based on the genetic algorithm that combining the characteristics of greedy algorithm and genetic algorithm has been proposed after presenting the theoretical basis of OCDMA technology.Compared with ordinary construction algorithm,this algorithm has higher diversity of the code word and faster convergence speed,which can provide basic support for future research.And then,we propose a new interference for the multipath effect on the indoor visible channel and derive the error rate of the system.The theoretical BER has been verified by Matlab simulation.The comparison between the BER of the whole system and the BER that considering only multipath interference shows that the OCDMA technology can effectively suppress the ISI caused by the multipath effect.Owing to the limitation of personal ability and time,this paper still has some shortcomings and improvements in further research work.Firstly,due to the fitness function used by genetic algorithm,the optical code construction algorithm proposed in this paper can obtain the optimal optical orthogonal code set only when the maximum cross-correlation value of optical code equal to 1.It is necessary to redesign the fitness function when constructing optical orthogonal codes with maximum cross-correlation value greater than 1.Secondly,the BER formula derived in this paper does not consider the influence of data transmission rate.In the future work,I mainly focus on the above two points for further research on this issue.