Design And Realization Of Viterbi Decoder In Free Space Optical Communication Based On FPGA

UV communication is a new wireless optical communication based on atmosphere absorption and scattering. There is no uv in sunlight near the ground for the strong absorption of molecule(particle), called Solar-blind, which reduces the interference to the optics source. UV commuincation takes UV in solar-blind section as carrier that modulated and loaded by the information electrical signal. The communication system transmits the signal through the free space and atmosphere channel, positioned and adjusted in the transmitter and receiver. UV communication is more confidential and much lower transmission power and more difficult to capture compared with the conventional communication. With such attractive features, UV communication can be employed in short distance,narrowband, power restricted and unattended sensor network on the ground.The atmosphere propagation channel becomes restricted and unstable when affected by the rain, snow, frog, cloud and onflow weather. There will be random errors or even burst errors due to UV signal attenuation, which affects the communicaion quality. To improve UV propagation characteristics, it must employ the channel coding technology. The paper proposes a FPGA designed method of convolutional code and Viterbi decoder based on research of the UV propagation channel module. The main research and work are as follows:①Review the UV communication history briefly, the potential applicaions, the advantages and disadvantages compared with the conventional communication, presents the popular channel coding technology, focus on the convolutional code and Viterbi decode.②Make a significant research on the UV propagation characteristics, present non-line-of-sight single scattering channel module,analyse the Luettgen module using mathematics methods and three different single to single NLOS transmission system modules, present the system performance parameters.Simulate, calculate and summarize the module through varied degrees.③Design the Viterbi decoder in VHDL language, employ eight-voltage quantum soft decision and parallel structure, improve the decode speed,present information storage and management to ameliorate the traditional register exchange method. Analyse and simulate Viterbi modules, download and validate on QUARTUSII. The paper presents a (2,1,7)Viterbi decoder based on the UV propagation channel, the circuit is simple which is pragrammed in VHDL language and downloads on the FPGA chip. It can meet the common UV communication. With the research and development of UV communication especially large capacity channel, it needs to employ more complicated decoder.