Research On Adaptive Diversity Technology Of Underwater Massive LED Array MIMO

In recent years,Underwater Wireless Optical Communication(UWOC)has become one of the important technical means of signal transmission in the water medium such as the ocean.Compared with traditional Radio Frequency communication and hydroacoustic communication technologies,UWOC has the advantages of higher security and bandwidth as well as lower time delay and less pollution.However,in the complex underwater environment,the beam propagation process is affected by underwater absorption,scattering,and turbulence.In addition,turbulence can cause jitter in the transceiver and lead to link misalignment at the transceiver end.To address the problem that turbulence and link misalignment lead to enhanced correlation between subchannels in MIMO systems,an underwater massive MIMO communication system with imaging reception is built,and an adaptive diversity algorithm is proposed to effectively reduce the combined effect of turbulence and link misalignment on the MIMO system.The main research works completed are as follows:(1)To address the problem of turbulence-induced random fading of optical signal,this paper uses space time block code(STBC)technique to reduce the effect of turbulence-induced random fading of optical signal,combined with chunking to improve the channel capacity of Massive MIMO system while mitigating the effect of turbulence.Firstly,the random fading coefficient of optical intensity caused by turbulence is simulated using a hybrid exponential generalized gamma distribution model,which is combined with an imaging optical MIMO channel model to obtain an imaging optical MIMO channel model under turbulent environment.The effect of turbulence on the MIMO system is reduced by performing STBC coding at the transmitter side and using the orthogonality of STBC coded symbols in time space.Then,the system channel capacity is increased by using the chunking process in combination with the imaging receiver while ensuring the system reliability.(2)To mitigate the impact of link misalignment on the system,an order successive interference cancellation(OSIC)detection algorithm based on interference minimization ordering is proposed in this paper.By analyzing the imaging principle of optical MIMO imaging receiver,analyzing and modeling the link misalignment channel caused by the relative offset of transceiver,and simulating the link misalignment error by using the transceiver alignment error obeying Rayleigh distribution,the channel model of imaging optical Massive MIMO system under the link misalignment condition is built.Based on this,the improved OSIC detection algorithm is proposed to first evaluate the degree of link misalignment and then demodulate the received signal with the least interference caused by the link misalignment by means of interference cancellation in order to reduce the interference of the system caused by the link misalignment.(3)The chunked STBC algorithm and the improved OSIC algorithm are used to solve the channel correlation enhancement problem caused by turbulence and link misalignment effects with different schemes,respectively.In order to simultaneously solve the problem of increasing sub-channel correlation of the system caused by the combined effect of underwater turbulence and link misalignment.In this paper,the adaptive diversity algorithm is proposed in combination with the chunked STBC algorithm.The algorithm uses the channel matrix to evaluate the link misalignment degree,and adopts different receiver-side detector merging schemes according to the link misalignment degree.Simulation results show that in a weak turbulent environment with a large degree of link misalignment,the system can still demodulate the baseband signal directly using the adaptive diversity algorithm without the need of MIMO detection algorithm,which reduces the receiver complexity of the Massive MIMO system.