Performance Analysis Of Hybrid FSO/RF Transmission And FPGA Implementation Of Coding And Decoding

Free space optical(FSO)communication,also called wireless optical communication,has the advantages of high data rate,no spectrum license,flexible networking,and high confidentiality.As a research hotspot in the field of wireless optical communication,FSO communication is susceptible to the effects of atmospheric turbulence and pointing errors,which severely degrades the system performance.Combined the FSO link and Radio Frequency(RF)link with hard-swtiching or soft switching mechanism,hybrid FSO/RF communication system can effectively improve the reliability performance of FSO link,which significantly deal the system availability problem in practical application.The research area for hybrid FSO/RF transmission scheme mainly include:threshold switching strategy between FSO and RF links,system modulation technology,detection technology and channel coding and decoding methods etc.This thesis considers the influence of atmospheric turbulence and pointing errors,focuses on the transmission characteristics of hybrid FSO/RF system using hard-switching strategy,and gives the FPGA implementation of LDPC encoding and decoding for FSO system.The specific works are as follows:(1)According to the utilization transmission character of the FSO/RF system,FSO and RF channel model were introduced with Gamma-Gamma distribution and Rician distribution respectively.Then the hard-switching transmission scheme for hybrid FSO/RF system was investaged with single and dual threshold under various parameters.(2)Based on the end-to-end signal-to-noise ratio of the hybrid FSO/RF system,the Meijer G function was used to derive the closed expressions of the system's outage probability and bit error rate(BER).Under the influence of atmospheric turbulence and pointing error,the outage probability and BER performance were studied and analyzed with OOK,BPSK,and DPSK modulation respectively.(3)For FSO communication system with heterodyne detection mechanism,theoretical outage probability and BER expressions for FSO/RF system were got by using Meijer G function.Then their performance were analyzed and compared with Intensity Modulation/Direct Detection(IM/DD)under different channel parameters.(4)By using QC-LDPC code as forward error correction method in FSO/RF links,the parallel structural encoder was designed with cyclic shift register adder accumulator(SRAA).The decoder with minmum sum decoding algorithm was described with partial structure.Then their FPGA hardware were realized and functionally analyzed.