Research On Performance Of Visible Light Communication Based On LDPC Code

As an emerging technology of wireless access technology in recent years, visible light communication(VLC) has attracted worldwide attention for its huge number of advantages including low energy-consuming, large-bandwidth, high security, non electromagnetic contamination and so on. With the rapid development of mobile interconnection and home intelligent, visible light communication will play an important role in it. Now studies on visible light communication are still in its infancy, and researchers focus on increasing transmission rate, modulation and demodulation, channel equalization, reliability and so on, and try to pursuit the visible light communication speed and capacity. With the rapid development of the VLC key technology and the dedicated chip, future VLC system will be toward the direction of the ultra wide bandwidth, ultra-high speed, large throughput, large coverage and high reliability including mobile big data and HD video on performance demanding. Therefore, we must find a VLC channel coding scheme of excellent performance, which will have a large throughput and be suit for high speed communication.The applications of LDPC codes in the VLC system have been researched. Firstly, the basic architecture of VLC system and channel model are introduced, and the optical channel are analyzed. The key parameters such as channel impulse response, the signal-to-noise ratio distribution and so on are analyzed using the simulation and the approximate model of the optical channel is obtained base on the simulation. At the same time, the light source layout is analyzed in theory and the best lighting layout principles are put forward according to the experimental simulation of different rooms. The simulations prove that the proposed source layout can effectively improve the receiving signal-to-noise. Then, the advantages and disadvantages of RS code in IEEE802.15.7 standard are analyzed, and the principles of visible light communication channel coding structure are elaborated. A QC-LDPC code is constructed on the basis of LDPC codes in IEEE802.16 e standard, and the fast encoding method is found. It is proved that there is no Girth-four in LDPC parity check matrix. Next, LDPC code decoding methods are introduced, and a low complexity decoding algorithm is improved based on BP algorithm and MS algorithm. The algorithm is applied to the simulation model of visible light communication system established already, and the channel with the worst channel conditions is found through the grid processing of the communication platform. And on this basis, the effect of iterative times and multiplicative factor on the BER performance of the system is studied. Finally, we compared BER performance and the calculation of the three decoding algorithm including BP, MS and the improved decoding algorithm. The results show that using the improved decoding algorithm can give attention to both performance and complexity. It is proved that, the constructed LDPC code can meet the structure principle of the visible light communication channel coding and it is suitable for the VLC system.