Analysis And Simulation Of Performance Using Advanced Modulation Formats In Fso System

Free space optical (FSO) communication is a broadband wireless communications technology, which takes the light beam as a carrier and the atmospheric space as the communication channel to achieve two-way transmission of information on broadband wireless communications technology. FSO combines the advantages of optical fiber communication and wireless communication, which has the characteristics of high rate, wide bandwidth, good security, convenience deployment and no restrictions on the frequency characteristics. So FSO has a good application prospect in solving the problem of’the last kilometer’, emergency communications, LAN interconnection and so on, what’s more, which has became one of the hot research topic in the field of optical access. But FSO system is easily influenced by the atmospheric channel characteristics, including the atmospheric attenuation, atmospheric turbulence and etc, greatly limits the transmission performance of FSO. Using advanced modulation can improve system performance, so the research of atmospheric channel performance and advanced modulation formats in FSO system is very essential.This paper has made a deep study on these issues and the main work and results are as follows:First we studied the FSO link system channel characteristics, analyzed the mechanism of action of the atmospheric attenuation, atmospheric turbulence and misalignment which impact on system performance closely, and took the mathematical analysis and derivation about this three effects.Second we compared the performance of OOK, PPM, BPSK and QPSK modulation in FSO system and according to the influence of the atmospheric attenuation, atmospheric turbulence and the alignment errors, we theoretical analyzed the received signal strength fluctuations probability density function of the channel characteristics in theory. And then using Meijer G function we deduced the BER closed expression of OOK, PPM, BPSK and QPSK four modulation formats.Third we studied the system performance with the different atmospheric turbulence, the different alignment error and the different transmission distance on FSO link when using advanced modulation formats. The results showed that: using advanced modulation formats can improve transmission performance of FSO system.Finally we proposed a hybrid FSO multiple signal transmission scheme and used the OPTISYSTEM optical simulation software to the system model, achieved a mixed-signal transmission which contain the BPSK, QPSK and UWB signals to verify the theoretical analysis.