Design Of PPM For Laser Communication In Atmosphere

The atmosphere laser communication is one of the most burgeoning methods for wireless communication, which sends signals using optic pulse. And its transmission rate is very high. PPM(Pulse Position Modulation), as one of key technologies in the atmosphere laser communication, arouses more and more attention by the virtue of high power efficiency and strong resistance to interference. The purpose of this thesis is to desigin a PPM modulation and demodulation system according to its characters.This thesis carried through the following aspects of study:1. According to PPM signal characters, the mathematics model of PPM signal is established and its PSD is analyzed in detail which is the principle foundation of the design of slot synchronization sub-system. Then power efficiency, bandwidth efficiency, and transmission capacity of PPM signal are intrduced.2. In allusion to the demand of design, the model of PPM modulation and demodulation system is put forward. And the principle and flow of the system are intrducued respectively. The model is the basis of design of system.3. The methods of PPM system design is introduced including PPM modulation system, PPMdemodulation and PPM synchronization system. And a PPM system is implemented by using DSP and FPGA which contribute to the digitalization of PPM transmitter and receiver.4. In this system, the DSP processor is used as PPM code, control of system,communication with computer, process of signals and transformation of analog signals to digital signals. The FPGA component realizes acquisition of slot clock and frame clock and demodulation of PPM. In this project, TMS320LF2407 is selected as DSP processor, and its software language is compilation. Verilog is hardware describing language of FPGA.In this thesis there are some emphases introduced as following: transformation of PWM to PPM, acquisition of slot clock by using DPLL, design of frame synchronization head utilizing Gold code, and detecting frame synchronization head by means of slow-and-correlation. The results of experiments indicate that the performance of this system is stabile greatly and the information can be modulated and demodulated correctly using the PPM system for atmosphere laser communication.