Research Of DPPM For Laser Communication In Atmosphere

This lesson is souceing from Xi'an university of technoligy's Youth teacher Special features and creative research plan,and the fund of Shannxi province department of education technology.It's also a subject of "Torch Plan",NO:2002HK52.FSO is a kind of technique that use laser as carrier wave to diplex transmit speech, data and picture information directly.The current atmosphere laser correspondence system designed with OOK or Manchester strength modulation/direct examination (IM/DD) method. Although this kind of modulation realized simply, its anti-interference ability is worse. For improving the ability of anti-interference ability, we adopted the pulse position modulation (PPM) in atmosphere laser correspondence system, however PPM improved anti-interference at the cost of bandwidth., differential pulse position modulation (DPPM) can make up PPM. Meanwhile, DPPM has a higher average energy utilization than PPM. For these reasons, we selected DPPM. The main content includes:1, Analyzed the channel and noise model that suitabled for FSO, and contrast analyzed several kinds of modulation that come from PPM..2, Analyzed the BER of DPPM signal, discussed the difficulties of implementing soft decisions and presented BER with maximum-likelihood sequence detection (MLSD), analyzed the power spectral density (PSD) of uncoded DPPM signal.3, Putted forward the schemes of hard decision and simulated it by use of Matlab.4, Accurately modulating and demodulating signal and clock synchronization were realized based on hardware language Verilog.In this paper, we expatiated on methods to remove or mitigate the nonuniform bit-rate problem. Detailedly analysed about storage. Proved by the result of experimentation: DPPM modulation/demodulation system with dependable performance and right logic relation. So it can complete modulation and demodulation in atmosphere laser correspondence.