Design Of MPPM In Atmospheric Laser Communication

Atmospheric laser communication becomes one of the hot spots in recent years. It has advantages of wireless transmission and abundant bandwidth of fiber. It has good outlook in sight communication, and has apllied in expansion of LAN, data return of wireless base station, temporary emergency communication and military secure communication. Modulation-demodulation is a key technology in atmospheric laser communication. Pulse position modulation (PPM) is usually used in atmospheric laser communication system. But, the information throughput in transmission with PPM depends so much on bandwidth. Multi-pulse position modulation (MPPM) can increase efficiency of bandwidth, efficiency of power and information throughput compared with PPM. Besides, it has better anti-jamming ability than PPM and people pay more attention to this modulation technology.The purpose of this paper is to analyze property parameters of MPPM, compare with PPM, find feasible mapping scheme and design modulation-demodulation system based on principle of MPPM. This paper mainly focuses on the following aspects:1. According to principle of MPPM, MPPM parameters were analyzed and compared with PPMS for the purpose of design of MPPM system. These parameters include the capacity of information transmission, transmission efficiency, bandwidth efficiency, etc.2. Expression of MPPM channel capacity with protective time slot was deducted. It was evaluated that channel capacity of MPPM changed with optical pulse power, reciprocal of system bandwidth and the average number of photon for single pulse. The performance of MPPM was compared with PPM in channel capacity.3. A new mapping method for dual-pulse pulse position modulation was presented basing on matrix theory. It converted binary code stream to MPPM symbols by using a general mathematic method.4. Three-pulse position encoder and decoder of MPPM are realized with Xilinx's FPGAprocessor.This project derives from Youth teacher characteristic and creative research plan of Xi'an University of Technology and the science and technology fund of Shannxi eduction department. It's also a project of "Torch Plan", NO: 2002HK52.