Research Of Satellite-based AIS System

With the development of the world economy,nautical transportation is flourishing,which in return raises high requirement fors in-time surveillance and communication of the ships.The former Automatic Identification System(AIS)can no longer satisfy the high requirement.Therefore,satellite-based AIS system is one choice for the high demands.The satellite-based AIS receiver greatly enhances the communication coverage,and it realizes in-time surveillance and communication for off-shore ships.However,the satellite-based AIS brings up some problems.Since it can cover several AIS communication cells,collision of the receiving signals will happen,as well as long time delay and large relative frequency offsets.In order to solve these problems,some scholars conduct researches on effective interference cancellation algorithms and the signal processing on the receivers.This paper starts with altering the existing satellite-based AIS receiver and proposes new methods to enhance the algorithms.This paper first analyzes the wrong bits happened in the satellite-based AIS signals during transmissions.And then,this paper concludes the character of the wrong bits after the separation algorithm.This paper proposes a 4-bit CRC algorithm.After Viterbi simulation,4-bit CRC algorithm is added to 2-bit CRC algorithm since location information is found to be useful during simulations.Results show that the packet error rate gets 1-2dB enhancement after 4-bit CRC algorithm is added.This paper also analyzes the method based on JMLSE,and find that 2-bits error happens frequently.Therefore,2-bit CRC is added to JMLSE algorithm and it shows that it brings 1-2dB enhancement for the packet error rate.Since the Viterbi algorithm has low requirements for synchronization,it applies to projects a lot.This paper proposes two methods to improve satellite-based AIS receiver.One is to take the advantage of the soft value information,which is the reliability for each bit.The soft values can help control the error from spreading.The other one is an improvement for receiving signal processing frame.This paper adds iteration of the interference cancellation,which helps to increase the ratio of the wanted signal versus the mixed signals,in order to lower the bit error rate.Simulation results show that,the combination of the two methods improves the bit error rate with 0.5dB.This paper shows that the combination of the CRC algorithm,soft-value based iteration interference cancellation will help to improve the receiver performance.