Design Of A Novel AIS Systems Based On OFDM And Research On The Key Technologies

Automation Identification System(AIS)is to identify the ship and realize the navigation at VHF.AIS is mainly used as the digital navigation of the sea-going vessels and to realize the automatic ship-shore communication.With more and more busy shipping business,a sharply increase in the ship users,leading to a serious shortage of the AIS spectrum resource and serious conflict slot.The transmission rate is 9.6kbps,it only can transmit the broadcast information,but can not transmit pictures,audio information,video information,and the real-time weather broadcast.So a novel AIS system based on OFDM is proposed in this paper;OFDM System is particularly sensitive to the Symbol Timing Offset(STO)and Carrier Frequency Offset(CFO),and a new blind symbol timing and frequency offset estimation algorithm based on the novel AIS that construct a normalized correlation function between the received signals is proposed;Aiming at the problem of the high peak to average power ration of the novel AIS system,a low complexity selective Mapping(SLM)clipping cascade algorithm is proposed.The details are as follows:(1)The novel AIS system including system parameter design,frame structure design,subcarrier start position design,SOTDMA protocol design.The link capacity and the transmission rate improve 6 times in the novel system,reducing the time slot collision problem under high load.The transmission rate reaches 67.2kbps higher than the existing AIS system.(2)A novel blind symbol timing and frequency offset estimation algorithm is proposed for,the method is to construct a normalized correlation function between the received signals.The proposed method gets the timing offset and the channel length from the correlation characteristics of the function directly.Consequently,the frequency offset is jointly estimated.The simulation results show that the algorithm has better performance under multi-path channel.(3)A low complexity selective Mapping(SLM)clipping cascade algorithm is proposed.The computational complexity of the algorithm can be reduced by about 35%.Meanwhile,the algorithm is most suitable,when the number of packets is ??128 M.The basic principles of SLM,improved SLM,clipping,and SLM clipping algorithms and their effects on PAPR suppression are analyzed in detail.Simulation results show that the PAPR of the new AIS system is 6.04 dB.The improved SLM clipping algorithm is superior to a single algorithm in PAPR performance;Comparing with the conventional SLM algorithm,the computational complexity is low.