| ALC (Atmosphere Laser Communication) refers to the two-way transmission technology of voice, data and image through laser beam in atmosphere. It has good application foreground in solve of "The Last Kilometer Problem" and emergence communication.In the atmosphere laser communication system, laser can be transmitted via atmosphere, because of being affected by many factors such as fog, rain, snow and atmosphere turbulence, BER (Bit Error Rate) increases. The key of application of ALC and realizing communication in the whole day is the ALC system could overcome the effect of climate. So, for the experimentation measure of error code characteristic is important in the ALC system.Firstly, the effect of atmosphere channel in the ALC system is analysed in this paper. Introduces transmit characteristic of laser and the effect of laser beam transmitting in the atmosphere.Secondly, the scheme and equipment of experiment is introduced in this thesis. Having an experimental measure under all kinds of weathers and the results of measure is detailed analyzed and discussed. The vast experiment data is used for establishing accurate model of the ALC system.Thirdly, four kinds of channel codes which are RS code, RS shorten cycle code, LDPC code and Turbo code, and the BER reduced by using the channel codes is introduced in the thesis. What is more, there are analyses about the performance among the four channel codes. Compare and analyses the performance improving of the BER in the ALC system.Finally, the simulation analysis of the BER of the PPM (Pulse Position Modulation) system has been done. Slot synchronization precision will affect communication system performance and the theoretical formula of BER is deduced.It's shown the effect of the weathers is great when laser transmit via atmosphere, but the system could communicate in an insight distance. So it is very necessary for improving the system performance in bad weather and it is a way by using the technique of channel code. |
PDF Full Text Request