Research On Optical Modulation And Demodulation Techniques In Mobile Atmospheric Laser Communication

This thesis investigates the pulse-position modulation (PPM) and demodulation technique in the mobile atmospheric laser communication system. The two outstanding advantages of PPM compared with on-off keying modulation are presented: higher power efficiency and extremely lower symbol error rate. Based on the analysis of the atmospheric channel and avalanche photodiode noise, the mathematical model of the output of the APD detector in the PPM receiver is discussed and the bit error rate of the APD detector is calculated and analyzed. The other three modulation schemes are analyzed, including on-off keying modulation, differential pulse-position modulation and dual header-pulse interval modulation. And the performance of these modulation schemes are compared and simulated on their signal pulse waveform, power requirement, bandwidth requirement, channel capacity and packet error rate. Optical modulation and demodulation implementation scheme in mobile atmospheric laser communication system are designed. The optical integrative access network transceiver system is discussed anddesigned. This thesis is organized as follows.Chapter 1 summarizes the development history and several key techniques of mobile atmospheric laser communication, draws a conclusion that it is an effective method to solve the problem of power attenuation applying PPM scheme, presents the developing status of mobile atmospheric laser communication in the world.Chapter 2 describes the basic principle of PPM scheme in detail, introduces its excellent power efficiency characteristic, analyzes the mathematical model of the PPM receiver and the performance of bit error rate of the APD detector, reveals the reason why we use PPM scheme in the mobile atmosphere laser communication system.Chapter 3 introduces the other three modulation schemes, including OOK, DPPM and DH-PIM, their performance are compared, simulated and analyzed.Chapter 4 presents the design of optical modulation and demodulation implementation scheme based on Chapter 2 and discusses some important aspects of the design concretely.Chapter 5 presents the design and implementation scheme of the optical integrative access transceiver which can integrate the 8XE1 PDH optical transceiver terminal and 10/100M ethemet optical fibre transceiver in optical fibre communication.Chapter 6 summarizes all the works of the thesis and put forward some suggestions to research optical PPM modulation and demodulation technique in the future.