The Application Of TCM In Atmosphere Laser Com Munication System

OPPM ( Overlapping Pulse-Position Modulation) is the modified form of PPM (Pulse-Position Modulation) and it extends the modulating signal set of PPM.OPPM has higher information transmission rate than PPM without the shrinkaging of optical pulse width.The extended signal set is not orthogonal anymore,which implies worse error probability performance.Some proper channel encoding technologies should be adopted to improve the system performance.Some coding gains can be achieved at the cost of the reduction of bandwidth utilization ratio for codemakings such as Turbo code and RS code.The contradiction of effectiveness and reliability of communication system can be released if some kinds of codemakings can obtain coding gains without the reduction of bandwidth utilization ratio.TCM (Trellis Coded Modulation) is a new kind of codemaking which designs coder and modulator as a whole module.The Euclidean distance of signal sequences can be increased from the proper mapping of convolutional codes and modulated signals.The anti-interference ability of system is developed and coding gains are obtained.The system performance has been improved from the compounding and optimizing of system interior instead of the reduction of bandwidth utilization ratio or power utilization ratio.It is a very significant research that apply TCM to atmosphere laser communication system.This thesis applies TCM to atmosphere laser communication system adopts OPPM modulation in order to improve the system performance at no penalty in bandwidth utilization ratio.The 8OPPM-oriented TCM system has been designed in this thesis on the basis of the research on PPM,OPPM modulation and the principle of TCM.The simulation result of TCM system shows that a coding gain of 1～3dB can be achieved with TCM and no bandwidth utilization ratio reduction.Choosing the optimal synchronizing sequence that can not received continuously from the TCM trellis as well as meeting the restrictive condition of self-correlation function.This method can decrease the probability of synchronization error.Then all of the modules of send and receive cell have been modeled and designed based on FPGA.The simulation result shows that the TCM system can meet the function requirement. Finally an experiment system has been established involves the integrated circuit validation equipment(with the XC2S200 PQ208 FPGA adapter of Xilinx corporation),laser,photoelectric detector,universal meter and logic analyzer.The test result shows that the two parties can communicate successfully.