The Search And Implement Of Reducing Peak-Average-Power In Free Space Optical Communication Multicarrers Modulation System

Transmission scheme of MCM(Multi-Carriers Modulation) is becoming more popular gradually,which apply parallel transmission mode. MCM can strongly combat multi-path fading and dispersive channel interference, increase frequency efficiency, and build up the ability of resisting noise.Therefore, it is a hotspot investigated in radio frequency communication at present. Free space optical communication has many advantages:great communication capacity,high bit rate,high security , broad bandwidth and good performance on anti-jamming. If we apply MCM technique to FSO communication,it will improve bit rate or reduce demand of apparatus rate, and it has advantages about decrease implement cost and complexity of communication system. If we combine the two techniques , they will exert each advantage, and avoid shortcomings. However,integration of the two techniques has some disfigurements as follows, comparing to single carrier technique.High peak-to-average power ratio (PAPR) is one of principle drawbacks of multi-carrier technique, which restricts its extensive applications .Because of information transferring uncertainty, lots of subcarriers peak are superposed and high value is produced, so that lasers are saturated ,which can damage lasers. The thesis mainly focuses on the techniques of PAPR reduction which is one of key techniques in multi-carrier modulation of FSO.We have achieved the following work:(1).The paper analyses why we adopt transmission scheme of MCM(Multi-Carriers Modulation), we introduce a particular channel characteristics in muticarrier modulation system of wireless laser communication,including atmosphere laser attenuation and multipath effect. And recommend structure and key techniques of multi-carrier modulation system of wireless laser communication. (2).The paper deduces the reason of PAPR , introduces definition of PAPR and probability statistics characteristic,and sums up all kinds of methods of reducing PAPR all over the world, including signal distortion technique, coding technique, symbol disturbing technique,and signal space extension. At final ,SLM and PTS method are simulated and analyzed by using MATLAB software.(3).A coding scheme based on Golay Complementary sequences and Reed-Muller codes is proposed to reduce the PAPR, and presented a particular procedure on encoding and decoding algorithm.(4).A algorithm of coding and decoding is particularly presented, and then stimulated the new method by using MATLAB software . And based on FPGA, we design the Golay Complementary code.Waveform simulation results prove the correctness of the design.