| As the construction of the Maritime Silk Road Economic Belt and information network facilities is strengthened,it has become a top priority to improve the emergency management level and information service capability of the ocean.Marine communication technology and the modeling of wireless channels are increasingly significant for the research and development of modern mobile communication technology.At present,Rician fading is a common fading form in marine radio wave propagation.However,the existing modeling method of Rician fading channel has the problem of difficulty in balancing accuracy and speed.In order to solve this problem,the existing model was modified and a high-speed high-accuracy Rician channel simulator was achieved by combining with the table look-up method.By comparing the accuracy simulation results with the traditional simulator,it was found that despite weakened randomness of the parameters of the high-accuracy simulator,the difference in accuracy between the highly efficient simulator and the traditional simulator was not significant.Meanwhile,this simulator had obvious advantages in balancing accuracy and efficiency.The maritime wireless communication system can be further explored based on the credible model of the channel.Currently,the maritime wireless communication system is dominated by VHF communication system,but the traditional VHF communication has relatively high BER and is susceptible to multipath interference.In this paper,the VHF system was improved by adding OFDM modulation and combining with the characteristics of OFDM modulation against multipath effect,so as to make it have certain advantages over the original VHF system in terms of different number of subcarriers and different levels of digital PSK and QAM modulation.As shown by the simulation results,through the use of eight 4-PSK or 4-QAM modulated subcarriers in a 16 k Hz bandwidth maritime VHF communication channel,the data rate and spectral efficiency of the system were improved by 2.37 times than the traditional VHF communication system.Besides,if 64 subcarriers and 64-PSK or 64-QAM modulation were used in the proposed system,the data rate and spectral efficiency could be 7.88 times higher than that of a traditional VHF communication system.In the offshore domain,due to the increased density of ships and improved number of connected devices between ships and shore,spectrum congestion could be triggered.Based on a plausible channel model,a radar communication(Rad Com)system integrating a MIMO system was designed,in which multiple antennas were used to receive and transmit multiple packets simultaneously,and multiple separated sub-links were combined to form many parallel packets,so as to solve the problem of spectrum resource shortage.On this basis,the advantages of radar and communication systems were combined to transmit vessel data of distance and direction detected by radar to multiple downlink users,in order to explore some of the roles in maritime vessel tracking and spectrum use.According to the azimuth simulation analysis of different methods,compared with the MMSE waveform and the circular algorithm based radar system,the synthetic waveforms acquired under the radar-communication system were less interfered in the side lobes and narrower in the main lobe width within the line-ofsight range of 5° to 15°.Moreover,the anti-interference ability was better. |
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