Design Of LT-Product Concatenated Decoder In The Visible Light Communication

Visible light communication(VLC)technology,which is green, low—cost, fairly good in security,without authorization of the spectrum, and can be combined with lighting, has become the industry's research focus.According to the concatenated codes scheme and considering the implementation, LT-product concatenated codes are used as channel coding for VLC. The coding algorithm, decoding algorithm and the degree distribution function of LT code are introduced. Analysis and simplification of the most fundamental and widely used decoding algorithm, Chase iterative decoding algorithm for product codes, modifies the factors of decoding algorithm and simulate the performance. According to the requirement of the OFDM system of VLC, the parameters of the LT-product concatenated code are determined. The optimal degree distribution function is designed for LT code. A feasible method for LT Decoder circuit based on BP algorithm with low complexity is proposed, and the search circuit is reused to reduce the complexity of the decoder. In the product decoder design, using the modified twiddle factor and scalding factor, so in the hardware implementation, multiply operation can be transferred into shift operation which can decreases the hardware consumption and improve clock frequency. Simplify the Euclidean value computation equation which makes the subtract operation and multiply square operation change into add and multiply. In the uncertain position locating module, the reusing and partial parallel working scheme is employed, this can makes the architecture simple and meet the timing requirement of system.After the complete design of the LT coder circuit and product decoder circuit, LT-product concatenated decoder circuit is designed.After the RTL design of the LT-product concatenated decoder circuit, the function simulation, FPGA verification and FPGA synthese of the LT-product concatenated decoder circuit are finished, and the results show that LT-product concatenated decoder circuit completely meeting the 2Mbps system data frequency, and the LT-product concatenated decoder circuit with low-complexity work correctly. Finally, the bit error rate of the LT-product concatenated decoder circuit show that the bit error rate completely meeting the system requirements. LT-product concatenated decoder circuit with low-complexity and good decoding performance can fully meet the requirements of VLC.