Design And Implementation Of Free Space Optical Communication System Based On GLRT

Due to the strong ability of high data rate,high channel capacity,low power consumption as well as strong anti-interference and other advantages,free space optical(FSO)communication system has been widely used in satellite communication areas.This paper makes a deep research on the performance influencing factors of the FSO systems in all respects,designing and analyzing the detection algorithm of received signal based on generalized likelihood ratio test(GLRT)theory.With the self-designed and manufactured experimental platform,which has very high practical value,the effect of the detection algorithm has been proved.At first the development situations,research statuses and future trends of FSO systems are introduced,followed by the detailed analysis of the theoretical basis and performance influencing factors,including system model,channel model,background radiation,etc.Then the ideally perfect detection and its performance expression has been illustrated,which makes a strong foundation for the design of decision algorithm.Secondly,basing on the in-depth analysis of the basic principle of GLRT and starting with the system and channel model,the decision metric of optical received signal is studied,which can implicitly estimate the channel gain without channel state information,making it robust and the key determinant of receiver detection performance.Utilizing the decision metric,this paper has researched the Viterbi-type trellis-search algorithm.In order to eliminate the error floor caused by all-zero event,the selective-store strategy is proposed.It can be seen in simulation that the performance can approach the genie bound.Then,to reduce the complexity of calculation for ease of the hardware implementation,decision feedback algorithm is designed.It can be seen in simulation that its performance loss is relatively low so that it also approaches the genie bound.Thirdly,this paper has introduced the overall designing scheme and parameters of FSO system experimental platform.And the general block diagram of analogy circuit and digital baseband circuit are investigated,as well as the design details,processing flow and implementation of each module.Analogy circuit includes transmitter part and receiver part.And digital baseband circuit,basing on FPGA platform,achieves the functions such as decision feedback algorithm,AD sampling,LPF,bit synchronization,hard decision,error rate calculation and so on.Then the design of a FSO communication experimental system based on GLRT is completed.At last,with the help of Chipscope and oscilloscope to verify the correctness,reliability and availability of the experimental platform,the function test of each module is performed.Then the experimental procedure basing on the FSO system is described in detail.And by the method of contrast experiment,the error performance of the system with decision feedback algorithm is verified to improve significantly comparing to that of hard decision.