Research Of LDPC For Indoor Visible Light Communication

Radio access network spectrum resources are increasingly strained and electromagnetic radiation is everywhere because of the popularity of "smart home"and the rapid spread of computers and smart devices.Inorder to achieve the broadening spectrum resources,green energy,removable access,visible light communication(VLC)emerged.LED lamps used VLC have the function of lighting and communications.There are so many advantages in Visible light communication technology,such as solid-state lighting,long life,high transfer rate,high security of data,harmless,low power consumption.Channel coding and modulation techniques are two key technologies to improve indoor visible light communication performance.In this paper,based on the latest research,we introduce LDPC which is widely used in wireless communication system into the indoor visible light communication.And Pulse Position Modulation(PPM)and Multi-Input-Multi-Output(MIMO)are superimposed.(1)LDPC is used in visible light communication system for the channel codec.The LDPC technique is researched from three aspects:the H-matrix construction method,Encoding and decoding algorithms.Furthermore,the parameters of LDPC are researched,including code length,bit rate,and iterations.(2)Combine PPM modulation with LDPC coding.It describes three kind of PPM modulations:single pulse position modulation,multi-pulse position modulation,differential pulse position modulation,analyzes the transmission power,bandwidth,and other characteristics of each modulation scheme.Although PPM can greatly reduce the power of the transmitted signal at the transmitting end,with the modulation order increasing,the bandwidth grows exponentially.Study on the performance of LDPC and PPM cascade system.LDPC-PPM system can not only reduce the transmission power but also increase coding gain.(3)Combine MIMO technology with LDPC coding.It describes Vertical Bell Labs layered space-time coding technologies(VBLAST)and decoding technologies of VBLAST.Decoding technologies of VBLAST include maximum likelihood,zero-forcing,minimum mean square error.Sutdy on the performance of LDPC and MIMO cascade system.The system can not only increase the diversity gain,enhance the reliability of the link,but also increase the coding gain.