Research On Signal Processing Techniques Of Space-based AIS

With rapidly development for global Information industrial,ocean shipping industry becomes more prosperous.Because of the trends of the increasing amount of ships and the density of ocean traffic,the safety of ocean environment is facing enormous challenges.In order to realize the high efficient ocean environment management,the traditional shore-based ship automatic identification system is unable to meet demand.Space-based AIS has the advantages of wide coverage and strong real-time performance,and as a result,it can greatly improve the efficiency of ocean shipping management.Space-based AIS system uses the advantage of satellite communication to realize the real-time monitoring and communication for long distance ocean shipping,however,this also faces a lot of challenges.Satellite beam can cover multiple AIS cells at the same time,and large relative speed is existed between Satellite and ships,so the high frequency offset and signal collisions are very obvious in Space-based AIS which have effect on the demodulation performance of receivers and the detection probability of system.To address these issues,in this paper,a Space-based AIS receiver system based on SOVA algorithm and a ship detection probability analysis model have been proposed.Firstly,this paper proposes a Space-based receiver system which is based on SOVA(Soft Output Viterbi Algorithm).In the Space-based receiver system where signal conflict is very obvious,Space-based receiver based on Viterbi has a poor bit error rate performance,however,on the basis of Viterbi algorithm,SOVA uses log likelihood information as the measure of path metrics calculation,and the path metrics introduce soft value associated with the bits decisions are use as the priori information of bits during the process of path research,and as a consequent,the performance gain becomes larger.This receiver system consists of SOVA demodulator module and the module of successive interference cancellation.The SOVA demodulator module obtains the bit soft output using the path metric difference between the survivor path and the competitive path,and performs Viterbi demodulation using the soft value information.The successive interference cancellation module detects strong signals one by one from the original signal and eliminates them in proper order until all signals are detected.It can be concluded from the simulation that the receiver based on SOVA can get better performance gain than the receiver based on Viterbi.Secondly,combining the demodulation performance of satellite receiver,this paper does the theory analysis,modeling and simulation about system ship detection probability.Firstly,it deeply analyzes the factors which can influence the detection probability of ships and the types of signal collision and the mathematic models of satellite observation time,observation range and signal propagation loss,etc.are given.Then,according to the type of the signal collision of the Space-based system and the system distribution model,we proposed signal collision probability theory model.Last but not least,considering about the ship detection probability model influencing factor,we can also consider the antenna gain and system demodulation performance to give a perfect and reasonable ship detection probability analysis model.It can be shown in the simulation result that the detection probability of the ship is more reasonable compared with the traditional model,which has important guiding meaning to the system performance.