| Free Space Optical communication has many advantages over traditional wireless communication and optical communication respectively. Such as frequency license free, large information capacity,non electromagnetic interference, high energy efficiency and convenient installation, flexible networking, portable device and well adaptability to emergent situation and short haul etc. In recent years, it achieved extensively concern, which mainly embodied in handle the problem of reliable and efficient transmission under space optical interference channel.The space channel effect on optical transmission signal is complicated sometimes even severe. It mainly consists of atmospheric extinction effect,fluctuation effect and deviation effect. Among them, fluctuation effect is the most pivotal research content. Thus the bit-error-rate (BER)performance of coded modulation system based on turbulent atmospheric channel is mainly researched and analyzed in space optical communication.The turbulence effect principally causes intensity fluctuation of different degrees. Qualitative and quantitative analysis on those interference help to provide a basis for subsequent coded modulation technology research.This topic is aimed at studying coded modulation key technology in FSO system under turbulent channel and proposing a good scheme with well energy efficiency, band efficiency and reliability. This scheme consists of two independent sub-schemes: A novel trellis coded overlapping amplitude and pulse position modulation (TC-AOPPM) scheme as well as a novel equi-different mapped amplitude and pulse position modulation(APPM) scheme. Among them, trellis coded modulation (TCM) are adopted as channel coding technology while pulse position modulations(XPPM) such as amplitude and pulse position modulation (APPM) and overlapping amplitude and pulse position modulation (AOPPM) as modulation technology. By theoretical modeling and simulation analysis,the novel high reliabile coded modulation FSO schemes based on the specific free-space optical channel and the minimal error decision theory can be researched.The novel points of this topic mainly lie in the improvements of the subset decoding metric and the compared uncoded AOPPM thresholds in the TC-AOPPM scheme, and the equi-different mapped amplitudes in the APPM scheme. A novel 4×8TC-AOPPM subset decoding method and a novel uncoded referential 4×8AOPPM scheme are proposed. The specific probability and statistical properties of gamma-gamma probabilistic model in turbulent atmospheric channel, horizontal correlation of AOPPM baseband symbols and the specific subset decoding procedures of TCM are taken into consideration. Meanwhile, a novel equi-different 4×4?4×8 and 4x16 APPM mapping scheme is proposed. The specific probability and statistical properties of gamma-gamma probabilistic model in turbulent atmospheric channel and the specific demapping procedures of APPM are taken into consideration. Then the above schemes are Monte-Carlo simulated. Referring to the simulation results, these two novel sub schemes under turbulent channel is qualitatively and quantitatively analyzed while its advantadge is also proved. Finally, the whole research work of the essay is summarized and the three main future research trends on key technology of coded modulation FSO system under turbulent channel are prospected. |
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