Research On Optical Modulation And Demodulation Techniques In Space Optical Communication

Compared with microwave communication, space optical communication has much superiority: much greater communication capability, narrow beam, good direction, much greater power density functions, lesser antenna size, and high capability of anti-electromagnetism and secrecy. Because of its high function-price ratio, under the condition of transmitting same information and same data rate, it is very fit for high data transmission ratio between satellite and satellite, satellite and space shuttle, and so on. So each country attaches important attention to space optical communication. Because high data rate and high reliability is the development direction of space optical communication, researching the modulation techniques and demodulation techniques become especially important.Firstly, the application foreground as well as the development trend about the space op-tical communication is introduced. Then the main structure, integral parts and detailed working process of the space optical communication are narrated especially, and the key technologies are also discussed. There are many modulation methods suitable for space optical communication, three modulation schemes are analyzed, including on-off keying modulation (OOK), pulse position modulation (PPM) and digital pulse interval modula-tion (DPIM). And the performance of these modulation schemes are compared and simu-lated on their signal pulse waveform, power requirement, bandwidth requirement and packet error rate. And describes the basic principle of PPM scheme in detail, analyzes the mathematical model of PPM receiver and the performance of bit error rate of APD detec-tor, reveals the reason why we use PPM scheme in the space optical communication sys-tem. Lastly, by means of upper bounds on the demodulation error probability and com-puter simulations, the properties are compared for the two demodulation techniques: maximum-likelihood searching for chips (MLC) and maximum-accumulating count searching for samples (MAS) and the effect of various parameters on demodulation per- formance are discussed, these results are helpful to designing PPM receivers.