Research And Verification Of Random Access In Sea Clutter Channels

The proposal of maritime strategy for a new era has promoted the development of maritime activities such as offshore wind power generation,offshore oil-gas field development and intelligent navigation.In order to provide convenient and reliable data transmission services for maritime users such as maritime equipments and offshore operators,various maritime wireless communication systems have been developed at home and abroad.As a key technology of air interface of maritime broadband wireless communication systems,random access,which ensures the orthogonality among the uplink multi-users,is the premise of the uplink communication link establishment.However,the maritime wireless communication system to be studied in the thesis has the characteristics of wide channel bandwidth,long coverage distance and fast movement speed.The existing random access scheme cannot meet the above design requirements.In response to this problem,the specific research contents of the thesis include:Firstly,according to the specific scenarios of random access under large bandwidth,long distance and large frequency offset,the influence of sea clutter channel on random access detection is analyzed,and the Longley-Rice model is utilized to predict the electromagnetic wave propagation loss under 6 sea state;Considering the multipath model of the diffuse reflection component,the effective diffuse reflection area is introduced to calculate the diffuse reflection multipath;for the key requirements of the maximum transmission distance of 50km and the relative speed of 80 knots,the acquisition sensitivity,multipath delay,round-trip delay and doppler frequency shift are calculated.Secondly,considering the large frequency offset characteristics of the sea clutter channel and the requirements of low complexity engineering implementation,an optimized random access scheme is designed.Aiming at the shortcoming of the general design scheme of random access preamble sequence against large frequency offset,an optimized preamble sequence design with anti-frequency offset function is proposed.The conjugate symmetric ZC sequence is used for time domain superposition,which reduces the influence of frequency offset on preamble detection.The Matlab simulation results show that when the SNR is-17.4d B and the normalized frequency offset is greater than0.32,the detection performance of the preamble sequence proposed in the thesis is better than that of the general preamble sequence.Based on the proposed preamble sequence design,the generation algorithm for the random access transmitter and the detection algorithm for the receiver are optimized for the purpose of low-complexity engineering implementation.Finally,the hardware platform implementation and performance test of the sea clutter channel random access scheme are completed.The interface and processing flow of key modules are given,the hardware resource consumption after placement and routing is analyzed,and a verification platform is built in the laboratory environment to verify the performance of the random access scheme designed in the thesis.The test results demonstratethat when the SNR is above-14.7d B,the error detection probability is less than10^-2,and it can cope with the arrival time uncertainty of 50km coverage and the maximum doppler frequency shift of 2.5 k Hz.The design scheme and verification scheme of random access under sea clutter channel designed in the thesis can be applied in engineering,and have certain reference value for the scheme design and implementation of random access with long distance and large frequency offset.