Research On RLL Encoding And Decoding Algorithm In Visible Light Communication

VLC?Visible Light Communication?uses the flashing of LED?Light Emitting Diode?to communicate.It has the advantages of high bandwidth,high rate,high stability,safety and environmental protection,and is an important research direction in the field of communication.The VLC system needs to transmit information on the premise of ensuring the flicker balance,but the information is susceptible to noise and optical signal interference in the channel,causing high bit error rate.Therefore,the coding technology in the VLC system needs to be studied.In the IEEE 802.15.7standard,VLC systems use RLL?Run-Length Limited?codes to convey information,and different scenarios require RLL codes with different run lengths.Commonly used RLL codes have a good flicker suppression effect,but the error correction ability is poor,and at the same time they cannot provide variable run length.Therefore,this paper mainly studies the RLL code coding and decoding method,and under the condition of ensuring the flicker control,designs the RLL code with variable run length and improves the bit error rate performance of the VLC system.The main research contents include:?1?By analyzing several RLL codes commonly used in VLC,the performance characteristics of RLL codes in VLC systems are studied.Firstly,the VLC model is built,and then the two decoding algorithms Viterbi algorithm and BCJR algorithm are studied,and the evaluation methods of the flicker characteristics and bit error rate characteristics are introduced.Finally,the performance of several RLL codes in VLC system is evaluated through simulation experiments.?2?For the problem that the existing RLL code cannot provide variable run length,a RLL encoding method based on the run-length limit as the constraint condition and the maximization of the free-distance as the objective function is proposed.First,the value range of the run length and the necessary state transition paths required by different run lengths are analyzed.Then,the output sequence is distributed under the premise of satisfying the necessary transfer path,so that the code meets the maximum value of the free-distance.Finally,the decoder is improved based on the Viterbi algorithm and the BCJR algorithm.The simulation results show that:under the premise of having the same minimum free-distance,the designed coding method can ensure flicker control,and the proposed codec algorithm has better bit error rate performance than traditional RLL codes.?3?For the problem of poor performance of the existing RLL code error rate,an RLL code encoding method based on FSM?Finite State Machines?is designed.First of all,the output sequence is divided into subsets with free-distance d_min=4 through the segmentation algorithm,then the sequences in each subset are assigned tothe directed weighted edges of the FSM graph,and finally the FSM graph is transformed into an state transition graph.The simulation results show that the designed coding method can ensure flicker control.Under low signal-to-noise ratio,the bit error rate performance is greatly affected by the number of states,and under high signal-to-noise ratio,the bit error rate performance is greatly affected by the free-distance and code rate.There are 37 figures,15 tables,and 75 references in this paper.