Research And FPGA Implementation Of Fountain Code For Helicopter Satellite Communication Application

Helicopter plays an important role in many fields due to its special characteristics,such as fast and flexible movement,vertical take-off and landing,and excellent carrying capacity.However,when the helicopter is far from the ground communication equipment or the ground communication network is destroyed,the traditional helicopter-ground communication will be damaged and unable to work any more.Satellite communication can provide high-quality data transmission over the whole global,which well compensates the shortage of ground communication.Therefore,the communication capabilities of helicopters in special scenarios can be greatly improved by combining the advantages of helicopter and satellite communication.Periodic occlusion of helicopter rotors is the biggest obstacle in the helicopter satellite communication.For this reason,the major issue of realizing helicoptersatellite communication is to solve the signal missing problem caused by the obstructions from the helicopter rotors.Among many anti-rotor occlusion communication technologies,the gap detection technology needs to accurately predict the position of the launch window and has high requirements for synchronization acquisition,the packet retransmission technology has low transmission efficiency due to the retransmission of all or part of the information,and the versatility of the two not good.The channel coding technology can recover the information of the rotor occlusion part and is independent of the rotor occlusion method.The fountain coding technology can make up for the shortcomings of the above two methods due to its unique erasure characteristics,but LT code has the problems of nonlinear coding complexity and excessive decoding overhead.Therefore,this thesis chooses the better-performing Raptor code formed by cascading LDPC code and LT code to solve the problem of rotor occlusion in helicopter satellite communication.The main contents are as follows:First of all,this thesis focuses on the performance of the LT code under the erasure channel,and discusses the optimal parameter configuration of the LT code under a specific number of original symbols by comparing several different degree distribution functions.The simulation results show that the system has better performance when the robust soliton distribution and the BP decoding algorithm are respectively used for the encoding and decoding.Secondly,this thesis discusses the performance of Raptor codes under the AWGN channel from three aspects: LDPC precoding,decoding algorithm and degree distribution function.The simulation results show that choosing an appropriate correction factor can help the normalized min-sum decoding algorithm obtain good decoding performance with low decoding complexity compared to the existing algorithms.However,when the code length is short,the traditional robust soliton distribution is not the best choice.For this reason,this thesis finds a better degree distribution function to improve the decoding efficiency of Raptor codes and obtain lower complexity.Finally,based on the project requirements,this thesis designs a set of communication signal transmission schemes based on Raptor code under the condition of low signal-to-noise ratio and dynamic occlusion of helicopter rotors,and carries out simulation verification and FPGA realization of key technologies.The simulation results show that the scheme can meet the requirements of helicopter satellite communication signal transmission under certain conditions,and the test results show that the communication link can achieve stable and reliable high-definition video signal transmission.